He is an A&M Alum. So if he wore a A&M jersey would that be an issue? I have been to many a ball park where the Anthem singer might say something like "Go Cubbies" or "Lets go Mets". I truly believe most kids in Mississippi State maroon believe the last five words of the national anthem are "go to hell Ole Miss". We have got to stop being offended where non is intended (or even if it is).
It'd have been fine if he had done something for his school and not "against" another school. CWS might wouldn't prefer it, but probably not anything that would cause them to do anything, unless they explicitly told him not to.
It's not a big deal. It's not like he was integral to the tournament. I doubt anybody knows who he is? He made the sign and CWS did what they had to do and he is joking about it. Had it been somebody that was not completely interchangeable with the next option, they probably would have had a different response. But it seems like everybody has more or less the right perspective.
And do the people that sing the national anthem for the school ever end it with go to hell ole miss? I would say they shouldn't do that even at an MSU hosted event, but certainly if they did that at an event hosted by a non-MSU affiliated/supporting group, I doubt they'd be invited back.