I dont think they're trying to be dishonest but are confused as hell and have someone working that don't know better.
My Petco is actually rather fishcentric and they carry 3 types of "moss balls", I was just there this morning looking at plants.
The floating ones attached to a weight, submerged ones, and marimo moss ball. The two first ones are like $4. The marimo is $8 or 9.
You can tell which is which by the density of it. Theres not individual fronds but more like fur. In your pic the fronds are obvious. Their return policy is good though so go back and see if they have the right kind. I find theirs are much bigger than any of the LFS in my area offer.
Halfmoon Double Tail