Assuming...what? Jesus could not possibly have been speaking about Gentiles, although Replacement Theology buffs routinely shove Gentiles into whatever nitch and cranny that fits their personal liking. Gentiles were dogs before salvation had come unto them after the middlle wall of partition was brought down. Scripture bears this out as a defense against the gross misapplications some apply to key verses isolated from a systematic study on the subject. There were many Jews in other nations of the world yet to hear His gospel.
MM
Jesus was simply stating what had been prophesied by Hosea and others. Peter later confirmed it was so by referring to this Hosea prophecy when he stated gentiles, who were not his people, are now his people. And Paul confirmed this to be true.
Yet the number of the children of Israel shall be as the sand of the sea, which cannot be measured nor numbered; and it shall come to pass, that in the place where it was said unto them, Ye are not my people, there it shall be said unto them, Ye are the sons of the living God. Hosea 1:10
But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light: Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy. 1 Peter 2:9-10
Even us, whom he hath called, not of the Jews only, but also of the Gentiles? As he says also in Hosea, I will call them my people, which were not my people; and her beloved, which was not beloved. And it shall come to pass, that in the place where it was said unto them, Ye are not my people; there shall they be called the sons of the living God. Romans 9:24-26
Gentiles are no longer dogs because God has cleansed them, and out of two people has made one: one flock, one body, one nation, one people, one law, one gospel.
And the voice spake unto him again the second time, What God hath cleansed, do not call profane. Acts 10:15