Nothing wrong with genealogies Nathi. The Jews based their claim to God's promises based off of their bloodlines and yet Christ had made a new way and a new covenant. Some Wanted to Judize the gentiles in the church but that simply created class society in the church which was quite contrary to God's will.
It could be because Paul called Titus his son. Titus 1:4 sais, "To Titus, Mine own son after the common faith.." I am sure there were unbelieving Jews who attempted to stifle Titus' job in Crete by saying that he was an illigitimate son of Paul. And according to the Law, this was a bad thing. It ws also an insult geared towards Paul. So I think this is why Paul told Titus to ignore such mindless banter.