The Thayan Menace said:
Granted, there are other possible explanations for this spell effect ... but a magical trap is the most logical.
Yes and no. Seeing what you said in print, the word "triggered" does suggest a trap over actual spellcasting. But at the gametable, with a battle going on at the same time, that word could easily be overlooked. And if it was, or if it wasn't clearly heard, then believing the spell to be the result of an invisible spellcaster is just as logical as a trap.
But that's really beside the point. For me, this all boils down to DMing style. As a DM, I tend to consider the game a cooperative one. Even though I'm running all the monsters, traps, devious villains, lascivious breadmaking neighbors, etc., I'm rooting for the PCs to win in the end. I don't pull punches (or the players would get bored), and I run a dangerous game, but still--I want to see the PCs triumph.
So if the players are missing something, like the fact that they're getting zapped by magical traps without even trying to Search for them, I'll start dropping hints, more and more blantantly with each trap that goes off unsearched for.
That's just me. Thayan Menace, you seem to be more neutral in your attitude toward DMing, which is perfectly fine too. From such a position, it makes sense that you wouldn't bother to remind players of their abilities, etc. (whereas I would.) Indeed, your players may prefer that, and I suspect they don't remind you of any
monster abilities you forget, either.
None of that's really important, though, since the actual adjudication has already come and gone. What's important now is where you go from here. If this person is your friend, then I assume you want to resolve this while remaining friends, both at and away from the gaming table.
Working under that assumption, I suggest that you simply tell him you're sorry that his PC died, you'll do your best to provide more informative descriptions in the future (even though you believe your descriptions are plenty-informative now,) and you hope he can let bygones be bygones as well, and continue to have fun with you at the gaming table.
The Thayan Menace said:
Besides, caving is not friendship ... self-degradation is not a sign of loyalty.
Regarding this quote, it's been my experience that sometimes friendship
is caving. It's sometimes putting your friend's wishes above your own. And yes, sometimes loyalty
is self-degradation, if it's for the sake of someone you're loyal to. But really, self-degradation is a very melodramatic word for what is, after all, a very, very minor affront to your dignity.