They should not have hired him to begin with... how was part of the interview process not finding out his involvement in the sign stealing, it has been a known thing for months if not years. I guess maybe Beltran lied to ownership, and that in itself is worth firing him for.
We do not know all the details and how Beltran as a player is different from all the other players who are getting no punishment.
But at the end of the day, I really did not want to see him as manager anyway...