But the fact is that he was completely right in his own sense because if your Talaffuz is not right while singing, it gets irritating.
OK. Let me come to the meaning. Talaffuz is an Urdu word, which means the pronunciation, articulation, the way of saying a word. In Hindi, you can call it uchcharan (उच्चारण). The word holds a real importance in music as in Urdu, slightly different way of saying a word may completely change it's meaning. For example Jaleel and Zaleel are almost opposites as Jaleel means having a splendor/style while Zaleel is humiliated, with no respect.
So next time someone says your 'talaffuz' isn't right, better take him seriously. :P