My immediate thought was also thrips, buuut with that many I would expect to see a lot of damage on those leaves, but I see none.
I suspect the leaves were overlapping and creating a little humid pocket and those are a type of springtail, which love humid environments and could have come up from your soil.
I would not go mad spraying anything as they are not really a problem. Just let the leaves dry and not overlap so much and they'll go back down into the soil.