No, that is not a normal operation. Or certainly not what I've observed nor what I would expect to happen.
Driving Mode (Eco, Normal, Sport) can have an impact on climate control (albeit depending on what settings you've used or changed). But not normally regen, as that is just the recuperation of energy whilst decelerating.
All that said, some have had issues with the climate in the new Niro EV where after a while it starts putting out cold air. There are various threads on this forum on that issue, so perhaps one of them has some pointers for you to try. It could just be timing/coincidence that when you set things back it triggered the correct heating/temperature.
The theory is, you set the car to the temperature you want, and select Auto with a fan speed of 1, 2, or 3. And leave it all alone and it does what it should do. Sadly, many of us find that isn't the experience in the real world.
You could try adjusting the use of "Auto Defog" and "Auto Dehumdify" in the climate options to see if that helps with your particular scenario. I am presently testing turning off the latter and will see how that goes over the next few journeys.