It's not unbelievable at all (the admittance, not the act, to clarify). In fact I'd say it's rather refreshing.
Firstly, these people work for Tesla. They don't work for Elon Musk.
Hoping it's not just me, but there is no way I'm lying to the cops (corporate cops, criminal cops, federal cops, whatever) to protect my CEO. Especially if I'm directly asked "Did you* do X" (* where "you" means "Tesla CEO"). Double-especially in this case where the "X" is "not Y" and the person doing "Y" actively avoided you making sure they did "not Y".
If it's my job to make sure my Boss doesn't do something illegal, and he actively circumvents my ability to do my job, damn straight I'm rolling over to the Feds.
Elon is the guy who fucked up, not Telsa. Whoever the FEC asked that question to at Tesla was probably not Elon himself, and the person on the receiving end of that question probably didn't want to lie to a fed.
This is the unbelievable part.
"We agree to NOT do X, under penalty of law."
[Does X]
"Did you do X?"
"yeah lol"