“An AR-15 style pistol”
Huh, what?
This is an AR-15 style upper and lower without the buttstock. Without the buttstock, and not shouldered, it's considered a pistol, and manufacturers provide uppers with short barrels under 16".
There's a fine line between a pistol in this configuration and a Short Barreled Rifle (SBR). Definitionally, an SBR has a stock that is shouldered and a barrel less than 16" in length.
There are certain items on the market like the SIG Brace that look like a stock, but isn't and isn't marketed as such which cause confusion.