The usual IF its Ryanair then they or the staff must be lying and over reacting and the Pax is always telling the whole story.
Passengers wanting to switch to something where he hadn't yet paid the bill for what he decided he hated.
Given he was Peed off already that his hot food choices weren't available and then ordered a sandwich and not paid for it, decided he didn't like it and wanted something else then not unsurprisingly CC decided enough was enough.
If having paid for it and it it unedible as he claims then CC as per FR crewmember has already pointed out its not an issue to change it, expecting to change something while still unpaid understandably gets a different response.