Besides which, I think he is pretty correct.
He's either correct or he's not.
Well, that, by itself, simply isn't true, especially when talking about GW rules.
And he's not.
Internet wide, you're actually in a minority opinion on that. Whether you want to go by obvious RAI (I do), view this immobilized+hull point as an alternate
form of penetrating hit (I do), or if you want to draw a somewhat interpreted distinction between effects that work "on hit" vs "on damage" (my favorite).
Regardless, it's certainly not certain, and while we may all have our own interpretations, saying, "No you are 100 % wrong because reasons" is just kinda......well it's ignorant, actually. Ignorant of all the reasons why that's NOT true.
Also, you were a jerk without purpose.