The shotgun was probably the wise choice for now because of limited .223 ammo at this time.
OP posted this back on Dec. 8th.
AR's were on sale for $900 at that time and ammo supplies were still good enough that .223 was a sale item in a lot of places, both places like Dick's as well as on-line.
Consider that now, the same AR the OP talked the guy out of buying at the time is going for a minimum of 1.5 times to 2 times what the price was on Dec 8th,,,,
I'd be pretty miffed if I were the original buyer that had been talked out of an AR.
I don't fault the OP for trying to help out. He was just doing what he felt was the right thing to do.