It's not as simple as calling it a correction, because there's such a thing as gambler's fallacy (even if there were to be a correction, it would be to what their baseline should be, rather than a full on recovery from the underperformance - i.e. if they're truly a .550 team but started out playing like a .400 team, they should be expected to play .550 going forward, not whatever it takes to get from .400 to .550 overall), but given that the RD/pythag and other related formulas have said the Cubs were better than their record way back when they were 10 games under .500 and they have proceeded to follow that up with this pretty unlikely-seeming run to get back to over .500, I wonder what changed other than predominantly luck.
But maybe it was just getting Mancini and Hosmer the hell out of here.
Also worth pointing out that they're at this point despite missing a decent bit of Steele, Bellinger, and Swanson's seasons.