I’m not sure what you mean about the food laws being added later. The dietary laws were part of the Law that Moses gave to the Israelites. He gave them much more than just the 10 Commandments. Exodus, Numbers, Leviticus, and Deuteronomy are chock full of the laws and regulations that God set out for Israel to follow, and the dietary laws were part of that.
Moses did tell the people not to add or subtract from the Law he had given them, but that means all of the laws in the Torah.
In Jesus’ time, the Pharisees were teaching that all the Jews must follow the Law, which was a good thing, unlike the Sadducees. But since it was practically impossible to keep the Law perfectly, they were making ways for people to get around the laws in their daily life. Father Simon had a good explanation of this in his Relevant Radio show on Aug 27th. For example, they would show people how to carry burdens on the Sabbath, or that only swearing by the gold of the Temple instead of just the Temple was a binding vow to God.
Father Simon says that the problem with this teaching was that by giving people a way to get around the Law, they would often stray farther from God in their hearts and focus on trying to get out of the laws as much as possible.
Jesus admonished the Pharisees for legalistically following the Law and teaching men to do so while their hearts were far from God. They thought the Law would save them and gloried in their “holiness” instead of trusting in God for salvation and giving all glory to Him. Outwardly, they were “clean” and had washed hands and bodies, but inwardly their hearts were unclean and full of evil. Jesus rebuked them for that disparity, because our hearts matter much more than if our hands are washed or not.