Do you think he will eat it?
A lot of children are not going to take a snack out of their pocket and eat it on a bus full of their friends who, if they don't get a snack on the way, will be asking what it is, why he has it etc.
He surely is getting a lot of attention for refusing breakfast isnt he?
I agree with exotic and other posters who say sit him at the table, serve the breakfast and say no more, just have a routine, no activities until after he has eaten, but you have to stick to it consistently for a few weeks otherwise it will not work
You haven't got anything to lose, he isn't eating breakfast now so a few weeks of putting breakfast on the table and not allowing any other activities until breakfast is over is not going to make any difference in terms of how much he eats.
I personally think that getting school, doctors involved is making this into a huge issue when it doesnt have to be.
As for being dismissive and indifferent- I have 3 DCs 2 are teenagers and I have found that putting rules into place and then saying nothing more, just telling them what I expect is far more effective than involving schools, bus drivers, doctors etc and asking them to solve a problem which is actually nothing to do with them.