Yes, that's how I realized it.
I used to make the exact same mistake, and it was really frustrating. Seeing the individual knitting and purling videos didn't help, but she explains it in the video showing you about going from knitting to purling. I'm just glad I kind of knew an answer to someone's questions. As a newbie knitter, this is a very exciting first! :-)
I had this exact same problem when I was trying the seed stitch. I started with 20, then along the way I realized I had almost 30 stitches! I was messing up when I switched back and forth from knit to purl.