I thought this a bit creepy when I read it before you posted..
I've always been fascinated by Orton. I love his plays.
It sounds like this awful murder was going to happen at some stage and perhaps Thornton was the trigger, but it could have happened with anyone saying the wrong thing.
It's a bit odd though that Thornton seems to want to claim the murder for himself...
ps: those alterations that Orton & Halliwell did in library books which they went to jail for, are very funny. Like works of art.