He is technically correct in that it is not an RNC rule for delegates.
**HOWEVER**
Most State parties bind the delegates they send to the Convention. And those States that do not bind their delegates, generally have the candidates select which candidates represent them in the so called “loophole” contests. (Illinois and Pennsylvania for example.)
So while he is technically (de jure) correct that no delegate is bound by convention rules, he is incorrect (de facto) due to the fact that all delegates must abide by their State rules as well.
Bingo!
State rules apply. Some states bind the *votes*, not the delegates, for the nominee. Delegates attempting to violate state rules would be appealed to the Convention Rules Committee, not the RNC permanent Rules Committee. Convention Rules Committee decisions have to be approved by a vote of the whole convention, which will be about 75% Trump and Cruz, if not an outright Trump majority.
Unless it has been changed since my copy of the rules, there is a provision in Rule 16 stating than any delegate bound by state law who attempts to vote other than the way he is bound will be considered to have resigned and his vote will be counted in the manner bound. It appears state law has been made the determining factor rather than a party rule. Some states bind their delegates for one ballot, others for two or three ballots. Some delegates are not bound at all.
“Caveat emptor (let the buyer beware) is clearly applicable to almost all information being presented in this political year.