Quadratus lumborum fascinated my massage therapist

Hi, all.
I went to a massage therapist for a half-hour massage for the very first time. Gotta say, loved the experience. Things were progressing with no surprises until she found my quadratus lumborum muscles. She was really surprised by how tight they were, and checked me for levelness in my hips (and was satisfied I’m OK there.) Man, when she worked those two muscles it felt like she was filleting them off of me. Well, it didn’t hurt/panic, but I am very glad I know how to breathe.
Of course, this is something I’ll be bringing to my yoga teacher, but for now my yoga teacher maintains a pretty materialist class. So here, I want to ask – what should I wonder about in the more subtle bodies as potential causes or effects for unexpectedly tight muscles running down my low spine?

ps – I would not reject advice regarding my physical body here. Just focused on the rest of it.