That is aftermarket. The cushion is what Yamaha has there, and the typical reason an owner removes that cushion is to allow use of that area as a walkthrough and hopefully avoid people stepping all over your cushions.
That's the reason I have it there, and we'll keep it there. It sounds as if that piece is dirty, it's typically not slippery, but there doesn't seem to be any way to tell, since we are only going on the description that someone fell while passing through that area, and it may or may not be related to a piece of SeaDek.
I can say this - the fiberglass decking, even with the non-skid pattern, can still be quite slippery when coming through that area also, so this isn't necessarily a problem with that padding
Pics of these types of things ALWAYS help, as there is absolutely no way to determine if someone is explaining the area right, and, to compare it with what someone who does not have this issue. maybe it needs to be cleaned, maybe it looks the exact same as a brand new piece, maybe someone believes their boat is pristine and to suggest otherwise is an affront to their character! Harumph!
Take multiple pics. Take close up pics, take pics of the entire area, take pics that show the general area of what you are trying to describe. Help US help YOU.