I can attest to this and I think it has to do with sucking in more oxygen in the process of vaping. You can get a bit light headed but your white cells are loving it!
While you are adjusting your desired temp for vaporizing marijuana you will draw loads of oxygen into your lungs which makes you high before you get the real thing.
It’s a lot smoother and you can’t smell it in a room. Plus it’s a lot better for you than inhaling 2000 degree smoke.