Why are they flying so close?

Many years ago I was a fish spotter off Cape Cod. I flew a C172 owned by another spotter; he flew a Decathlon. Both of us were former Air Force pilots who were flying fighters in the guard. All of our spotting was in VMC, so I didn't really need instruments, nor did I trust my instruments enough to fly a precision approach. Late one afternoon we were returning to the Cape when the weather was reported right at Cat I ILS minimums at Hyannis. My initial plan was just to divert down to Long Island, but then he asked if I wanted to fly the approach on his wing. I said sure, and tucked up on his right side. We added the word "flight" to the call sign, and got cleared for the approach. We broke out right at minimums, he took the left side of the runway and I took the right, and we rolled out in formation. As we came into visual range of the tower, the controller was incredulous. "Five six alpha whiskey, are there two of you?" "Affirmative." "Did you just land like that?" "Affirmative." "Is that allowed?" "Affirmative." "Uh, OK, taxi to the ramp."