I don't see the problem. Pringle was using a definition of the fantastic that included supernatural horror, as many critics do. The expansive definition is frankly more defensible and less arbitrary than one that attempts to categorize a work by whether it's "scary" or not. For the record, James Cawthorn and Michael Moorcock's "Hundred Best Fantasy" similarly includes classic works of horror such as Shirley Jackson's HAUNTING OF HILL HOUSE and Fritz Leiber's OUR LADY OF DARKNESS.
Here's that list - not sure if it's in order:
Gulliver's Travels by Joanthan Swift
The Castle of Otranto by Horace Walpole
Vathek by William Beckford
The Monk by Matthew Gregory Lewis
Frankenstein by Mary Shelley
Melmoth the Wanderer by Charles Robert Maturin
The Narrative of Arthur Gordon Pym by Edgar Allan poe
A Christmas Carol by Charles Dickens
Wuthering Heights by Emily Brontë
Moby-Dick by Herman Melville
Uncle Silas: A Tale of Bartram-Haugh by J. Sheridan LeFanu
Alice's Adventures in Wonderland and Through the Looking-Glass by Lewis Carroll
Flatland by Edwin A. Abbott
She by Henry Rider Haggard
Doctor Jekyll and Mr Hyde by Robert Louis Stevenson
The Twillight of the Gods by Richard Garnett
The Story of the Glittering Plain by William Morris
The Picture of Dorian Gray by Oscar Wilde
Dracula by Brom Stoker
The Turn of the Screw by Henry James
The Man Who Was Thursday by G.K. Chesterton
The House on the Borderland by William Hope Hodgson
Black Magic by Marjorie Bowen
Zuleika Dobson by Max Beerbohm
A Princess of Mars by Edgar Rice Burroughs
Tarzan of the Apes by Edgar Rice Burroughs
The Lost World by Arthur Conan Doyle
The Night Land by William Hope Hodgson
Herland by Charlotte Perkins Gilman
The Citadel of Fear by Francis Stevens
A Voyage to Arcturus by David Lindsay
The Worm Ouroboros by E.R. Eddison
The Haunted Woman by David Lindsay
Lady into Fox and A Man in the Zoo by David Garnett
The King of Elfland's Daughter by Lord Dunsany
The Ship of Ishtar by Abraham Merritt
The Trial and The Castle by Franz Kafka
With Wood by John Buchan
War in Heaven by Charles Williams
Turnabout by Thorne Smith
The Night Life of the Gods by Thorne Smith
Dwellers in the Mirage by Abraham Merritt
Zothique by Clark Ashton Smith
The Werewolf of Paris by Guy Endore
Lost Horizon by James Hilton
Northwest Smith by Catherine L. Moore
Jirel of Joiry by Catherine L. Moore
The Circus of Dr Lao by Charles G. Finney
Land Under England by Joseph O'Neill
Conan the Conquerer by Robert E. Howard
At the Mountains of Madness by H.P. Lovecraft
To Walk the Night by William Sloane
Roads by Seabury Quinn
The Once and Future King by T.H. White
Slaves of Sleep by L. Ron Hubbard
Caravan for China by Frank R. Stuart
Fear by L. Ron Hubbard
Darker Than You Think by Jack Williamson
The Case of Charles Dexter Ward by H.P. Lovecraft
Land of Unreason by Fletcher Pratt and L. Sprague de Camp
Conjure Wife by Fritz Leiber
The Book of Ptath by A.E. van Vogt
The Dark World and The Valley of the Flame by Henry Kuttner
Titus Groan, Gormenghast and Titus Alone by Mervyn Peake
The Exploits of Engelbrecht by Maruice Reichardson
Mistress Masham's Repose by T.H. White
Adept's Gambit by Fritz Leiber
The Well of the Unicorn by Fletcher Pratt
You're All Alone by Fritz Leiber
The Dying Earth by Jack Vance
The Devil in Velvet by John Dickson Carr
The Tritonian Ring by L. Sprague de Camp
Three Hearts and Three Lions by Poul Anderson
The Sword of Rhiannon by Leigh Brackett
The Broken Sword by Poul Anderson
The Lord of the Rings by J.R.R. Tolkien
The Golden Strangers by Henry Treece
The Great Captains by Henry Treece
The Haunting of Hill House by Shirley Jackson
Stormbringer by Michael Moorcock
The Serpent, Atlan, The City and Some Summer Lands by Jane Gaskell
The Crystal World by J.G. Ballard
Black Easter and The Day After Judgement by James Blish
Rosemary's Baby by Ira Levin
A Wizard of Earthsea by Ursula K. Le Guin
The Green Man by Kingsley Amis
Neither the Sea nor the Sand by Gordon Honeycombe
The Philosopher's Stone by Colin Wilson
The Pastel City by M. John Marrison
The Infernal Desire Machines of Dr Hoffman by Angela Carter
Red Shift by Alan Garner
The Compleat Enchanter by L. Sprague de Camp and Fletcher Pratt
The Alteration by Kingsley Amis
Our Lady of Darkness by Fritz Leiber
The Drawing of the Dark by Tim Powers
The Sending by Geoffrey Household
The Colour of Magic and The Light Fantastic by Terry Pratchett
The Businessman: A Tale of Terror by Thomas M. Disch
Hawksmoor by Peter Ackroyd
Expecting Someone Taller by Tom Holt