It should be legal to lie to the FBI especially a massively corrupt treasonous stooge like Mueller.
.
The FBI deliberately lies during their questioning to get their victim to lie.
So what did he say?
“My cell is comfortable and the food is good?”
I have no idea why these people talk to the FBI at all. What purpose could be served? They are going to charge if they have the goods and not charge if they don’t. And, if there is specific info they want and will give something for it, it can be communicated through an attorney which makes the truth or falsity irrelevant unless the lawyer knows it is false and then it is the lawyer’s problem.
I’d tell them to F off.