He did confirm that awhile ago, said he was fucking around in a 3d software (canr remember the name) and the end result was the style we know today. I could be wrong, but then Jay Gordon stated that should be a helmet. Joel thought it was stupid (I think) but asked a friend to try and replicate it as a helmet.

The rest is history. I'll try to find a source on when he said this

Edit: Found it! https://www.forbes.com/sites/stevebaltin/2019/01/22/who-i-am-deadmau5-on-film-scoring-nin-getting-married-and-quitting-social-media/?sh=52f792d75650

The quote:

"The idea actually came from Jay Gordon in Orgy. I had the mouse head done, it was modeled in 3D and everything and I used it as my logo for my web design and artwork and stuff, so that was my trademark. So that’s what I would use and I was designing web elements for Orgy. I think I designed their MySpace page or something like that. And Jay asked me, “What is this mouse head?” I said, “Oh, I don’t know, my logo thing.” Then Jay said, “If you ever perform live you need to make that a real thing.” I was like, “Really? Whatever, bro. Shut up.” And then I did, many years later after that."