Either there is more to this than meets the eye, or your former boss is an idiot.  
The only person who would know how simple a trick is is someone with a bit of magical knowledge (not necessarily what I would call a 'magician', judging from his behaviour) and frankly the very last person I would trust were I in your former boss's shoes is a potential rival.
"A magician who knew how your trick was done said he saw how you did the trick. In spite of the fact that he is a magician (as far as I am concerned) and quite clearly a massive loser, the customer's word is final. Oh and he also claims that you, a magician, did a trick in part of your act, so it's doubly bad."  Crackers.
That reminds me, I must get David Copperfield, Derren Brown, Lance Burton, Penn and Teller, Criss Angel, Paul Zenon and David Blaine fired.  If Paul Daniels were still on TV, I'd get him the sack too.  I've seen stuff when they've performed, often in really simple tricks, so they can't be any good.   
On the other hand, maybe you simply weren't ready for this particular gig.  I am not just thinking about your technical standard (but in my view, absolutely anyone can have a bad day), but also your age and confidence generally.  Just get performing again with some small, easy things, and build yourself back up.