As a staff your line manager humilities you infront of a guest whats your best reaction at that moment bearing in mind he didnt enquire whats wrong?

Patience at that moment, as Boss is always right. if he/she wants to prove you wrong. then you are wrong. Later on he/she will realise and discuss and you can clarify. No need to argue, you will never win.

Without mistake or mistake’s confirmation nobody humiliate .

If it’s happened by mistake than Wait for your turn…. Discuss & clarify things about reality.

Never react or take decision immediately. According to yours question he already done(Immediate Reaction)…..But don’t become guilty by doing the same .