wardens can sense other wardens (e.g. anders in the deep roads), so alistair loghain and stroud should have called out thom. (not to mention the inquisitor - he says he hears the song in front of the other warden and then that he doesnt in skyhold). overall the false calling must have caused a lot of confusion if that slipped somehow. or bioware forgot their own lore again
I mean, yeah. I’m pretty sure Thom was deliberately written so we’d notice inconsistencies in his story.
But I’m happy to accept the false Calling as the reason Alistair or whoever the warden contact is didn’t notice the lie. Same thing happened in The Calling, where you’ve got a warden who stopped being able to sense the darkspawn because the song was so loud:
The humming had eclipsed any sense he had of the darkspawn. Any attempt he made to reach out with his mind to sense where the creatures were found only a wall of beautiful sound instead. Like a weed, it had insinuated itself into his consciousness, blocking out anything useful.
So Alistair might not be able to sense other wardens over the sound of the Calling. It’d be completely in keeping with their lore.