well I know there's 2 kinds of olive snails, one's that are more cool water guys and ones that are more for our systems. not sure what kind yours is though! I'm sure someone else will be able to chime in on this as I'm not too good on actual specimen ID's! lol I can just tell you what kind it looks like. lol
as far as diet, not too sure either, I've always heard olive snails were predatory, but then again, I may have heard it from a bad source, never know. I'd keep an eye on him for a couple days. it was like that big giant snail I had, remember him?? well he died as I didn't have what he wanted in my tank except algae and seemed algae wasn't part of his diet I guess! lol