So he flipped. Just like all of the rest.
They have a choice here... They can (a) tell the truth or (b) go to jail and hope the truth never really comes out so they don't hit with more charges even though they know everyone else will spill the beans.
This is exactly how it works. They do their investigation and figure out what the truth is. It's not difficult; All of them are leaving behind a paper trail or digital trail. (Hell, Cohen fucking recorded Trump talking about paying off Stormy Daniels LOL.) Then they interview people under oath, and when they catch them in a lie Mueller and his team tell them what they know the truth is, and threaten to charge with perjury AND other crimes... At that point they can either tell the truth, or go to jail.
Every time we turn around everyone is lying.