Legion near Judea at time of Jesus

[Frank]

And also if it was an auxiliary unit wouldn't the commanding officer be a praefectus praepostis?

As explained above, an auxilia cohort was commanded by a praefectus cohortis, a praepositus cohortis or a tribunus (roman citizens). Every auxilia cohort had 6 (or 10) centurions. These centurions could be romans or non-romans. So just the use of the term "centurio", does not qualify the unit as legionary cohort.

And as Nathan already mentioned the original greek text does not proof the use of legionary cohorts.