What mode is this? Freeway speed, electric on

An odd thing happened to me as I entered the freeway the other day. I was accelerating up to freeway speed, when I realized that I didn't really have my foot that far down on the accelerator, yet I was making good gains.

I glanced at the screen and noticed that in addition to the gas engine being on (orange arrows), apparently the electric motor was also on (yellow arrows).

I was surprised to see that the electric arrows were on... they weren't just flitting on and off like they do when you are cruising at freeway speed (assisting)... they were ON all the way, and for some time. I flicked the 'INFO' button on the wheel and noticed that the battery was all green, save one bar. Flicked the 'INFO' screen back, and still both orange and yellow arrows are on. At this point, I was probably going about ~62mph.

I can't recall how the moment broke... whether I lifted my foot off the accelerator ever so slightly, or whether the car just 'broke' the mode, but then the car was just in the 'regular' freeway cruise mode, where the engine is on (orange arrows), and the electric motor assisted (flitting yellow arrows once in a while).

During this acceleration phase, my mpg's were well over 50, which I never get when I'm accelerating, especially on the freeway.

So, I'm wondering..... what mode is this? Did it happen because the battery was full? I don't recall reading about this, but maybe I just haven't read enough.