He is the person who has witnessed Pre nup issue by Ishwari. Just think about that father, how scared he would be. He still agreed to this marriage for Sona's happiness.
He has tried accept Dev but now he is faced another big lie of Dev. Think it from Bijoy's point of view, he saw her daughter being happy and accepted by dixits for the first time. Remember what was Ishwari's reactions and staements when Dev stayed overnight at Bose house or at Dev's bday. Think how insecure he is as father. Now that insecurity is back again and for him its only Dev who is responsible for it.
Dev din hide infertility issue for neone else but for himself bcoz he knew if this fact will be known to Sonakshi and Ishwari, marriage wont happen. He din think what will bose family will go thru. He was desperate to get married to Sonakshi. If at that time truth would have been out Sonakshi would have refused to marry Dev and Bose family would have supported each other as a unit.
For bijoy this lie is not less than a bomb blast on him, so this dialogue does'nt uncalled for. Being a daughter's father Bijoy is absolutely right
My point of view