Pain flare generated during exercise?

I've really been doing a good job with resuming normal exercising and activity. Yesterday, during a resistance training session I was doing some lower body squats (single leg, bodyweight) and during one rep in could feel my low back on the left side tighten. I didn't continue to push to avoid making it worse but I was left with this question:

I know my chronic low back pain is TMS (and I had all but eliminated it!) however in a flare like this, is the pain from the physical?