It is not a big thing if he came to know Sidhi went to hotel,he is expected to do that much research for the case but about their consummation, how the hell he knows and no one in the family does, not even Seema..
I was also surprised by Kunal's surprised look when thakral says Sidhi has gone to hotel.I thought Kunal knew she had come to hotel, that night she was screeming at the top of her voice that after what I have seen, heard , I cant stay with you , he even asked her what have you seen, heard ...so y this surprise expression now.