Great job on it!!
Yep, you're knitting through the back loop which twists the stitch. It's a valid stitch that is used on some decorative patterns as well as if someone needs to tighten up a loose stitch. Combination knitters use it, too. To untwist you'd have to do the purl differently. You'll also want to learn how to do the decreases and increases differently. Here's some info if you're going to knit combined.