Ji Yao who never ever said this word to anyone out loud felt so stupid as he watched his father gloating like he had won great award. Ji Wen was acting like a parent who had just heard their baby say their first word. He wasn't even this excited when Ji Yao actually said his first word.
Ji Yao couldn't help but glare daggers at him but it had zero effect on the proud dad. This proud dad even went as far as trying to hug him but Ji Yao actively dodged. If Ji Wen hadn't been gloating for the past few minutes he would have hugged him but the man just had to go on and brag to his ancestors.
As to why Ji Wen chose this moment to compel him to say what he said? It was because when Ji Yao was young and Ji Wen had regained his state of mind and started trying hard to raise his son well he had said I love you to Ji Yao a dozen times but the kid never said it back.