They shut down before the law required them to (by a few hours), and now they’re back despite no changes in law or action by the president. Biden had already issued an executive order, nothing changed
That would be my question also. You can't explain the shutdown as following the law if the law didn't change between the time of the shutdown and coming back on. It seems to me like the more accurate assessment here is an anticipation of policy changes, which however fruitful do not reflect any change in law, but perhaps some change in the degree of reassurance that the law won't be enforced.
If it's not that, it may well be as the original commenter in this thread suggested a stunt to make a point.