These days it's hard to tell and there's always a mix of both with any high demand items so it makes the stock limits even more pronounced. With how Valve has done hardware releases lately though I imagine it's more a stock limitation.

I also got one and didn't think scalpers were the problem at the time. I have since seen eBay listings of people trying to sell the controllers (that they don't even have yet) for 3x the price, though, so they maybe did play a role. There was a limit of 2 controllers per Steam account and they sold out within 30 minutes, so not sure if bots were used or what. There wasn't a lot of time to mess around. I've seen a lot of people who wanted one couldn't get one. Personally I added it to my cart about 2 minutes before the official start time and then it took 12 minutes or so of retrying to actually check out.