I wasn't aware a reaction is a 'right.'
Khalid made several public appeals for support, which he requested in the form of letters to Rep. Sue Kelly, Sen. Charles Schumer and Chairman Lamar Smith. He made those appeals based on "how important it is for me to run for the United States".
I would say that those fans who supported him in his application, based on those statements (support sufficient to allow his application to leapfrog ~ 1 million others) do have a right to feel let down by his subsequent actions, even if those actions are understandable from a professional and athletic standpoint.
It's a simple human interaction. If you ask me to do something for you, and promise certain things in return, I have a right to feel aggrieved if you do not fulfill that promise. Do you believe that those fans and supporters would have written their letters if intead Khalid had said "how important it is for me to make a pot of money"?