Good point.
In HH his helmet’s visor provides him with capabilities similar to Demon Sight.
The question is, does the visor have Truth Sight? In ITA, he would not have had his helmet on, but one would think if it had truth sight, he’d have put it on.
I sort of think it does not do “truth”
Big reason is, what if he were to use “Truth Sight” on everyone in Mount Doom talking to him? He would almost have to decide it was broken, or seriously question his entire life (which he is doing anyway but..)
Now, this raises another question. What happens to people who “Truth Sight” Tizzy? My guess is that everything he says, even if obviously a like registers as true.
Actually, I wonder what standard clerical wisdom is in regards to Truth Sighting a demon. I am going to guess that the consensus is that it doesn’t work with demons, because when the demons told the truth, the clerics would not believe it, so therefore would assume Truth Sight did not work on demons.