Well gee, there was a face he hadn't been expecting to see-- but then there was very little about Kuja that was predictable, something of which he'd quickly learnt during his time fighting in the war.
But the war was over now, right? And while he still couldn't remember much about his life at all, Kuja was one mark he could never seem to forget.
Except-- he wasn't quite sure how he felt about that. Kuja wasn't all too bad, really; and while they'd fought on numerous occasions (both having lost their fair share of said battles on eventually equal groundings) Zidane couldn't say he hated him. Couldn't say he disliked him either-- he was just... wary. For good reasons.
If there was one thing he did know, however, it was that he didn't want to fight. Not any more. The war was over, so what would be the point of it?
Anyway-- what was he supposed to do other than stand there looking half confused and half defensive? Say 'hey it's been a while'? Nah, Zidane had a feeling something like that wouldn't go well at all. He'd probably end up getting laughed at, for one.