This. The video Don't Talk to the Police[0] has several concrete examples of how not taking the fifth amendment can be to your disadvantage.

[0] https://www.youtube.com/watch?v=d-7o9xYp7eE

This is not a criminal proceeding.

But the case has been referred to the authorities for a possible criminal case. In that light, there may be more reason to keep quiet.

It's one thing to take the fifth out of an abundance of caution when all it might do is raise some suspicion. It's another thing when doing so is likely to cost you $250MM. It's hard to look at this course of events and conclude that Levandowski probably did nothing wrong.