If true, what it really tells me is that Mario is not the strategic mind I'd hope he could become. It's a very short-sighted move.
First off, let me preface this with saying I'd be shocked if he went elsewhere. By all accounts, he turned down both Schiano and Chud for the Miami job.
Secondly, I think it would be short-sighted for anyone NOT to check all their options. If someone came at me with a possible job offer, even if I'm comfortable and happy with where I'm at, I'd be an idiot to not listen to what they have to offer. I'd actually question his intelligence if he didn't go through with an interview if they requested one, unless Golden explicitly blocks him from doing so.
And last but not least, he wouldn't have done this without informing Golden. You don't burn your coaching bridges for a "possibility."
It's one thing to listen to an offer over the phone. It'd be another thing altogether to fly over to really listen to the offer for another job about a month after you took one. As an employer, it'd make me wonder about your objective.
I guess I can see that with regards to the short time frame in other industries, but coaching is so fluid and jobs change so rapidly, that I don't consider this much of a red flag for assistant positions. If I had the choice between coach A who is ambitious and looking to advance his career and coach B who is happy to remain as is, I'd go with coach A every time (all things equal).
A couple more things that makes this easier to take for me is 1. This is a position coach we are talking about, not the HC, which to me would be a no-no if he's looking one month after landing a gig. 2. It's Cristobal. He loves the U too much to put them in a disadvantageous position. If he does leave (which I'd be shocked if he does), he'll do so in conjunction with Golden (meaning he wouldn't leave him up the creek with no **** paddles).