I actually think it depends a lot on what he was doing while on the phone.
Sending personal texts - could wait so rude.
Tweeting his run for his fans who couldn't be there - part of the new way technology is used and not rude.
I disagree with this. Ceremonies should have the participants' full attention, specially in a large, visible role. If a ceremony is relevant enough for someone to participate, it should be important enough to give it your full attention. If it isn't, then you don't consider it an honor and should turn it down (or, if for some reason you can't turn it down, then it is important enough to someone that you should at least pretend). He could have had an assistant tweet for him while did the run, tweet himself immediately before and after the run but not during it.
Unfortunately, this is hardly without precedent. Athletes take pictures and use a cell phone during opening and closing ceremonies. The parade queen is up there taking pictures instead of interacting with the crowd. And so on. When you take on this kind of role, it isn't about your experience, exactly. You are there as a symbol of something.
If this kind of behaviour is frowned upon when it is done by an audience (whether in church, theater, class or meeting), it is even worse when it is carried out by the main lead.