So I've seen OH bins closed by FAs and PAX before they are full but yesterday I was boarding a UA A320 from ORD-LAX and as my wife and I approached row 7, the FA closed two bins on the left side that were empty. It seemed rather random to us as:

• We were early to board [so it didn't seem to be motivated by getting things ready to go]
• The rows in the vicinity of row 7 weren't occupied yet [so it didn't seem to be motivated by having PAX put bags above their rows]
• F passengers had already boarded and were seated [so it didn't seem to be motivated by saving space for F cabin]
• He did not do the same to the bins on the right side

It didn't affect us in any way (We just opened up the bin and put our luggage in), but it just struck me as odd. As I've said before, I've seen bins closed when 85% or even 50% full, but never when 0% full and so early in the boarding process.

Any FA insight into why one might do this, or is this just a futile attempt to find reason in a chaotic flying world?