I'm not entirely sure.... You'd lose a tiny bit of timing precision triggering off of a sine wave, lower slope means variation in trigger level sensitivity can manifest as jitter, but you'd be able to adjust the trigger level to hit different phases of the same signal (or have multiple triggers, maybe?) And if it really mattered and you needed a sine, you could just filter it on the input side and be sure. I've yet to see a piece of an equipment with an input that specifies one or the other, but maybe they exist.
As for the listing, it could be just that it's an old one - I think ebay lets some sellers list an item for up to a year, so maybe they were originally selling the older model and then just didn't notice that it changed or didn't remember to update the description. There seem to be a lot of sellers that sell stuff in a lot of genres, so maybe they don't really know much about it.