One possibility is that, since fab3 were denied from practising in the space aryaman has got them somewhere out in some another studio. They are practising there and then Manik who has suffered memory loss but has not forgotten his music may be practising with some other band who may be practising there and so he comes there. But since Nandini has been hallucinating about Manik so she thinks that she again doing the same hence smile on her face and fab3 and aryaman are shocked to see him.
Second possibility is that 2 scenes are clubbed one scene is where fab3 and aryaman are practising an madhyam comes there everyone is shocked to see him and Nandini is not because she has asked him to play the main guitarist and the second scene could that Manik is practising with some other band and Manik enters there and not here where fab3 and aryaman are practising.
May be Manik has forgotten his past. In the promo they show he hears fab5 concert news so maybe he feels connected with fab5 so he goes to concert to see their performance and when they finish their performances he moves out from there.
Guys what are your opinion about this