I remember looking this up a while ago, and came across this in the EoFF wiki

WikiEoFF | Main > TidusAndShuyinAnAnalysis

But sufficed to say, Shuyin died 1000 years ago, a very emotional death one can be sure. His emotions bound themselves in his pyreflies, and most of which ended up in the Den of Woe (where we see a shadow of Shuyin playing havoc with peoples minds) and of which fragments can occasionally get out. One such pyrefly happened to be flying through DZ at the time Tidus was being created, and the result was that Shuyin's appearance and abilities got duplicated in Tidus.

I find it highly unlikely that Tidus is a direct replica of Shuyin based on the fayth's memories since he was 1000 years separated, and one would think that DZ would emulate life sufficiently well to result in mixing a parent's features into their offspring, bar any external influence, such as stray energetic pyreflies...

That's if I understood that wiki article right