Those fruits do look very similar. Sugar Apple is Annona squamosa. The name Custard Apple is mixed up depending on where you are. Here it's a hybrid of Annona squamosa X Annona cherimola and is the main commercially produced one. Annona reticulata is also referred to as Custard Apple (and sometimes so is Annona squamosa).

I have a brown one which should probably be Annona reticulata, but that is supposed to have a very 'ordinary taste'. Mine has a good taste, so don't know.

I've tasted the frozen food. The taste isn't great. I know it can be rather confusing with all those names .. lol, but like what Andrew Zimmermann (TV host for Bizzare Foods) here always says, "If it tastes good, eat it!"