It's only a cultural issue if it's on a tee-shirt?
If the removal of the tee-shirts was the result of a cease-and-desist from Oceanic Arts, it's possible they were made aware of the tee-shirt and not the mug. "Hey, I saw someone at Whole Foods sporting our #428 New Guinea Mask." I doubt anyone at Disney would inform them that they were also selling a mug. Not while it was still in stock, anyway.
Has anyone tried reaching out to Oceanic Arts on this subject?
Whatever the reasoning behind the removal of the shirt, neither it or the mug have anything to do with Grog Grotto. The mask is featured in Trader Sam's Enchanted Tiki Bar in CA, but not at the Grog Grotto here in FL. It was a bad design as far as Grog Grotto merchandise is concerned.