Apparently not, without exercise but exactly the same food (same batch and portion), the rise the day before and the day after were 0.72 and 0.94, seems the exercise was the main factor. I even had fairly similar sleep.
Having done some reading, my understanding is that high intensity workouts cause the brain to think it's in fight or flight mode and it sends the signal to release glucose into the blood and it releases more than you can use. Steady cardio type workouts don't have this effect and can reduce bs.
As I'm obese, to be honest ANY exercise is better than nothing and I do need cardio work anyway so this will be my way forward for a while rather than trying to ride the tour de france (well for 20 minutes). Swimming worked well too, no change in readings.