Very doubtful that it was the BB because the way it is threaded, the act of pedalling tightens it. More likely I am guessing your freehub is on it's way out. It attaches to the rear hub body and contains the mechanisms that were once contained in the freewheel.

I've stripped a few out over the years and this is how it starts. Unfortunately, there is no easy way to test this. You can keep riding and it may not happen again for a while. But, if it completely fails, you will be stranded.

You can replace the freehub. The easiest, cheapest way I have found is to buy a low end Shimano hub and use the freehub. Remove the axle and the freehub can be removed with a 10mm allen.