Yes thats not likely that orange order members would send their children to an Irish language school. But it's very probable that non-religious family's would send their children to non-denominational education.
Who said 93% of the kids were against a united Ireland? Again i will repeat myself, a small sample of 15 students in a school. That school had maybe around 800/900 pupils.
You are making the assumption that many make based on a guess, the same as i would have done, but then i quickly realised, through that experience, that attending an Irish language school doesn't translate to wanting a united Ireland for all pupils.