When children are screened for kindergarten interventions, the aim is to err on the side of intervention. No one was ever hurt by a little extra phonemic awareness, right? It's also usually based on a five- or ten-minute screening instrument, which a four- or five-year-old could easily blow off for any number of reasons, as Ametrine pointed out. If you were in for just a few weeks, you were probably there just long enough for the school to reach a scheduled re-screen or progress monitoring date, at which point you tested out. Or if you missed the screening date altogether, for some reason, the school could not, by law, keep you out of school, so they may have played it safe, and placed you into the intervention group until they had a chance to do your screening. This often happens with late move-ins (which can actually mean any time after March of the spring before kindergarten, in some places).
If you have no memory of struggling (rather the reverse), I would chalk it up to the usual adjustments of the first few weeks of school, instead of a significant error.
