There is nothing in old covenant law that prohibits believers from visiting Gentiles or eating with them. Old covenant law restricts the food that may be eaten but not the company. No doubt there were additional expectations alongside these laws which meant that Jews generally considered it to be inappropriate to eat with Gentiles and/or visit in their homes as a result of their being a potential source of ritual defilement.1 These are likely the laws/traditions which Peter has in mind.2
28 And he said to them, “You yourselves know how unlawful it is for a Jew to associate with or to visit anyone of another nation, but God has shown me that I should not call any person common or unclean.