I think we might be agonising over the wrong two words, Horror and Thriller are not comparable, Horror is something a film (or book or whatever) is, while Thriller is something a film does. If a piece of art is essentially seen as a message with a sender and a receiver, one is implied and the other inferred.
The good Doctor is right, Thriller is an adjunct that can be applied to other genres, or indeed anything. Thriller is a bit like Shocker or Drama and can almost be thrown into any description, tabloid headline style, to sensationalise and add colour.
I feel its use is somewhat gratuitous or tortologous, it merely means "not dull".
One of the most iconic historical uses of the word was to describe a piece of non-fiction, a boxing match in The Philippines, whereas The most iconic use of the word is the title of the most successful music video of all time, which is directed by John Landis and features zombies, werewolves, transformation and creature effects and many other "horror" staples... so the etymology gets nicely confusing when we look at historic labels and comparisons.
I think that what we might actually be struggling to differentiate between is Horror fiction and Crime fiction.
(Both capable of "thrilling" or failing to do so)
Just looking at last August's films I can see the grey area;
The Dead, Damned by Dawn, 13 Hours, are clearly all horror fiction,
Red White and Blue, The Tortured, F, are arguably crime fiction,
but when it comes to I Spit on Your Grave, Dream Home, The Loved Ones, it becomes a bit tougher to call,
and I'm not even going to try when it comes to A Serbian Film.
If we look a bit further back than last August we can see where and why the two genres began to overlap so significantly.
"Crime fiction" as a literary genre has been pigeon-holed longer than "horror fiction" and it was crime novels that people used to read for the gritty, visceral shit that has you checking you locked the back door properly. In the old days of Penguin paperbacks it was crime that was put in its own seperate category with green rather than orange covers, and in early film it was the crime/noir titles that were more disturbing and adult in nature than the really rather tame Universal horrors.
There were exceptions, but generally the "crime novels" with their distinct green covers (much like Italian giallo's with their distinct yellow ones) were seen as "the hard stuff"; intended for adults and not for the faint hearted or those of a nervous disposition, a frisson of taboo and controvercy coming with the alure of the dark side. We dare you to read...
The two genres co-existed and overlapped for some time (and still do), horror fiction more often having a supernatural element and crime fiction having a mystery (or "whodunnit") angle was the only crude thematic rule of thumb to differentiate between them.
As books gave way to film (and later video) as the zeitgeist media, "horror" has become the new umbrella term for "the strong stuff on the top shelf" and "crime" has become more respectable as it's audience has gotten older and society's bar for shock and compassion has risen. (Midsomer Murders isn't top shelf stuff, and isn't horror either, despite all the decapitations and other spectacular deaths, its just too morally safe)
The transition from Crime to Horror, as the handy label for "the heavy shit that'll fuck you up", probably began with films like Hitchcock's Psycho and was firmly cemented by the arrival of the Videonasties, which brought new levels of top shelf taboo and stigma to the birth of home entertainment. We dare you to watch...
When it comes to Frightfest and what makes a Frightfest film, it's not a matter of being a horror film per say (or being chosen by the organisers), I think it's about films that push boundaries, test limits and upset censors, adults only and strong stomachs may be required, a little taboo, a bit of controvercy and a certain amount of "are you fucking kidding me?? a human fucking centipede!?! where do they get this shit?!!"
In short; Frightfest films belong on the top shelf with the hard liquor, hunting knives and porn, and if you belong to a catholic confederation of concerned parents, they aren't likely to be your cup of tea.
That is what Frightfest, and "Horror" has come to mean for me.
I've come here to chew bubblegum and kick ass... and I'm all out of bubblegum