Last time they fought Dire he was KOed by a measly 123 damage, and only 21 of that was delivered before that Guardian fell. Even if we're accounting for some additional damage he might have taken fighting Sarris off panel, I doubt he's rocking 500+ hitpoints now.

I think the most likely explanation is simply that he healed himself between the encounter with Ardon and the current encounter with the Sons, which would put him at losing 167 so far. This is all assuming that all the combat is happening on panel. He could be healing between panels for all we know.

Of course, it's also assuming that he even has stats.