Basically, it's a system that looks at stuff that got answered, but where the answers didn't get much votes, and gives them a chance to be upvoted/downvoted rather than staying lost in the ton of other questions, never to have eyeballs on them again.
It sucks to have written a good answer that just happened not to have attention, and it sucks to have non-answers/low quality stuff that did not get downvoted or flagged as it should have been. This bumping of old posts is there to prevent that.
As for the "how", it's done automatically, following the criteria on this answer to Community ♦ seems to be bumping new questions more frequently than usual on main Meta:
Note that the posts eligible for bumping are those scoring >= 0 that have gone at least 30 days with no activity, have at least one non-deleted answer scoring 0 and none scoring more than that, and no accepted answer (also, they can't be deleted or closed).
There's a pretty reasonable chance that you just didn't have very many questions meeting those criteria until today...