The truth was that Gao Tianji was shocked by the performance, and composure of the young Chef in front of him. From what he knew this was just an extremely talented young Chef and nothing more.
Surely the food he cooked was great, but that was nothing to take notice of or to be handy to him. The only possible good point was that he was able to enter the Young Master Gao Jian's room easily.
If he had any need of actually sending someone to poison or deal with the Young Master without getting involved he might have thought to use him.
But he didn't have that need anymore. After all, he had already killed the one that didn't agree with his plan, and the one remaining had already taken care of it.
It was impossible for his blood daughter to actually try and do something without his permission and approval. So he already knew about Chef Guo's work.