It's probable that the Argonian was simply a very talented armor smith who could make Bonemold.

We find out later on from the Armorer's Challenge, a book in TES IV, that one of the greatest armorers who ever lived had been an Argonian. It seems this may be an obscure racial talent that's not expressed so much in character creation but which nevertheless is part of Argonian culture.

The Armorer's Challenge was in TES III as well.

Ah, that was one of my favorite books. It has that classic TES irony.

I don't think that's the case in Morrowind, though, since most slaves seems to have translations of their own names. Eg, while they still have a name in their owners language, it is not a name of the the owners culture.
But that answers nothing.

But that specific name is Dunmeri and that slave is Argonian. Maybe the master just wanted to name his slave with a Dunmeri name. Since the master can pretty much do what they want to with a slave, it's very possible. As the name does translate into Great Benefit, maybe he was a extremely good slave, with a fairly kindly master.

Well, we do not know what language the word belongs to. It doesn't sound very dunmerish to me. Well, at least not the "gah". "Julan" does, I must admit. In a completly hypthetical example, if the inventor of that armor style were an Argonian named Gah-Julan, it is not completly impossible that his name did not mean "great benefit" originally, but since it were of "great benefit" to the Redoran, it first became a "concept", and then later, became so inseparably associated with it, that a new meaning were imposed on the original words. Stranger things have happened.
Though that is of course stretching the limits.

And on the topic of the slaves name, if he was named "Great Benefit", I think it would rather be because of the rest of the slaves calling him that, because of his brown-nosed attitude.

So it was...and that only serves to strengthen the implication.

And Gah-Julan is a Dunmer name? I'm sorry, but I don't see it.

It may be of Ashlandic origin... remember, some of them are known to wear Bonemold, and Bonemold is really just a technologically superior and more hardily crafted chitin armor.

But Gah-Julan wasn't a resident of Morrowind.

Also, it states in The Armorer's Challenge that, unlike in-game armor, real armor, mostly when custom crafted, wasn't created from only one type of material. Gah-Julan's competitor used a variety of materials to craft his set, so I'd assume that Gah-Julan might've done something similar. The bones Black Marsh are probably of different constitution that the bones of Morrowind.

Gah Julan doesn't sound like a Dunmer name?

Don't forget St Jiub.

Some Dunmer names don't follow either modern 'Settled Dunmer' conventions or the older 'Velothi' (actually Assyrian, fact fans) style. There's a few scattered around in MW. Rare, but there.

Also I think 'Gah Julan' fits well enough when you compare some of the older Dunmeri settlements on Vvardenfell: Maar Gan, Gnaar Mok, Khuul, Gnisis. None of those are much like the Velothi or House Dunmer names, but that doesn't mean we've strong grounds to assume those names have an origin in Dwemeri, Nordic or Akiviri - or Argonian.

I didn't mean to imply that an Argonian actually invented Bonemold...only that the one in Morrowind with the same name as the armor may be a talented smith who can craft it. Hence his being named after it and by extension its creator.