Petty will also have flatter profile as it does not have enough blade height for more belly. The gyuto can be both. Grind - everything is possible there, really. If the petty is meant as a short suji it may come with more pronounced convex (or wide bevel) profile so that it minimises friction on meat. If the petty would be ground too thin it would quickly become too 'bendy' as the blade lacks the height. The gyuto can be very thin where it counts while still be reasonably thin. Just my opinion, of course.