The 2 firearms were in his possession when he was arrested.
The article isn't clear but my understanding is that he was arrested sitting in his vehicle outside of his mother's house. The police then searched and found an arsenal of 11 firearms at his residence.
The short-barreled shotgun was found in the house.
The Wayne County Sheriff’s Department were contacted. Deputies obtained verbal and written permission to search Conway’s residence. Eleven firearms were discovered, including handguns, shotguns, and rifles of various calibers. Among the firearms seized was a Winchester 12-guage shotgun that had its barrel and stock cut; the barrel measured nine inches in length.
Unless there were
two short-barreled shotguns. You're right that the article isn't clear.
But what do you expect from a reporter who can't spell "gauge"? I lament the sorry state of journalism.