One of the few firearms that’s been conspicuous by its absence in the extensive SIG SAUER lineup is a .22LR pistol (SIG would probably prefer that you purge the GSG-made Mosquito from your memory bank). So when the decision was made to add a new rimfire semi-auto handgun, SIG made the entirely reasonable decision to built it from the ground up using the P320 general blueprint.
Unlike the dearly departed Mosquito, this new compact-size pistol isn’t an outsourced product.