This is not a valid argument, because the two events were very different.
In Garland, TX it was an event guaranteed to upset Muslims. The event organizers, very prudently, hired guards to keep the events safe. An attack was expected, guards were there, and it was resolved successfully.
In San Bernardino, CA the attack was unexpected. While having CHL holders might have helped matters, we cannot be sure. People are much easier to attack when they think they are safe. Therefore, this comparison is invalid. A better comparison would be to an unexpected act of violence, such as this one.