To my knowledge I've never seen titanium rust, I didn't think it was possible. So that narrows it down to stainless. They were "chrome/silver" color as well, and titanium doesn't come that color. Different looking texture too, as titanium really sticks out usually.
Titanium I would imagine might oxidize, but I still doubt that, and I'm quite certain it wouldn't ever rust either.
But they don't make aquarium application stuff to my knowledge out of titanium (other than chiller parts) since titanium is so rare and expensive unless it's REALLY REALLY NEEDED (like chillers, as stated before).