I suppose it's left up to us to guess.
(SPOILERS)
I just assumed it was like a supernatural random matching - Phil was desperately looking for a woman and Annie was apparently, desperately looking to escape her marriage and in Twilight zone fashion they were 'mind-linked' and she seized the opportunity to lead him on.
i thought it was just out of her desperation.. and his loneliness.
it could explain it.
although i thought the episode would end similar to Bradbury's "The Silent Towns" where the one dude meets the lady, whose voice he heard over the phone, and finds her gross.
he then runs the f*** away..
this was a great ep of TZ. mustve been part inspired by Last Jedi!
couldve ended in any number of twists - it wasnt the woman in the FB pics but some hideous looking woman, or he was the creepy looking guy she was talking about on the train, or he goes there kills the guy and its the wrong house ..all had me guessing until of course the finale ended in the most devestating ending possible lol