I think it's very believable that thapki falls in love first. She didn't have much experience with boys in the past and I think except from her brother, purab was the first guy who actually noticed her kind heart not her stammering problem and also he was always super kind and caring towards thapki and her sick mother. As for social status, puab being a famous singer son and a music company CEO, is in much higher class than thapki, and on top of that, he is handsome and hot too. Thus our poor thapki has no other choice than falling for him. As for Purab, he definitely likes and respects thapki but I'm not sure if he loves her yet.