Of course it is. You have no way of knowing what would have happened if President Bush had sent the bill back to the House. You can speculate, but you can't ever know.
Vetoing kills the Bill.
You'd be hard pressed to find a law that passed with a smaller than veto-proof majority that eventually overode a veto.
There is absolutely NO WAY CFR would have been overriden.
Saying Bush signed it because a veto would have been overridden is simply absurd, and untrue.