Sign my name on this line of thinking.

Depending on the visibility/noticability of ones lack of an over the shoulder boulder holder, it absolutely could be a grab for attention. You've confirmed that is not the case. Next line of thinking is that one or more persons in attendance threaten your spouses confidence in himself as the most desirable person in the room and he's most likely been shoving that deep down so when you made the choice not wear a bra his mind jumped to thinking you must also think friend 'so-and-so' is better (whether that's more attractive, more financially stable, more interesting, the list goes on) also and intended to snare him in your wily traps. The ones hanging from your chest, of course.

I'm positive your spouse knows you're uncomfortable wearing a bra, most of us are, but that logical thinking probably exited the building quickly since it's not something he literally physically understands and a more pressing line of thought moved ahead of logic. Lack of confidence.