That's not the point. The point is he hadn't done anything. The game should know that.
He said he had no idea that the Thalmor would send people after you, that's what the bit you quoted was a response to. Yes, the Thalmor do send out squads and patrols to "deal with" anyone they don't like.
Whether or not the player is one of those people for a known reason or it just happens randomly, I don't know. I don't think I've ever been attacked by them without having given them a reason. Some people believe they have been attacked for no known reason at all. Either, way, the squads do exist.
but the letter seems to state the player had done something specific to Thalmore interests to piss them off. Its not really good enough.
Yeah, when you don't know of anything you've done to get their attention, it kinda leaves you scratching your head.
I'm starting to wonder if it's possible that visiting a Talos shrine and (perhaps) leaving an offering there has anything to do with it. We do know that they stake out shrines to spy on and accost worshippers. But that's probably a long shot.