It looks a quite high-quality vinyl (or as we call it: "vegan leather" ) if it is vinyl. I tend to agree with you that if it were leather, they'd probably say so.

Apparently it's made by Selle Italia, fwtw.

I'm a little unsure about the shape, since I'm quite knock-knee'd. I'd prefer a more definitely T-shaped one. And one that provided perineal pressure relief. But it seems to be the best one I've found so far that's (probably) not leather.