They appear to be upset because someone is selling 3d printed Darth Vader helmets on Etsy. It's not clear if the OP is referencing physical 3d prints proper or just STLs.
I would assume the OP feels that these prints or files are copying or using someone else's work (well, beyond Brian Muir's, since any reproduction Vader helmet is copying that worthy's work), possibly their own, but this is also unclear. Without further details it's impossible to evaluate the claim of "stealing," since of course anyone who sets out to recreate the Vader helmet all on their own is going to end up with a very similar final product and could well duplicate some details found only on reproductions, if the seller/file creator relied on references taken from a reproduction. But at the same time it's not unknown for people to take STLs they found on the web and print them for sale on Etsy, so either case is plausible.