My only guess is that some of the THC is absorbed orally, but in a small quantity. That might explain the high feeling. Can't say I would know what the mechanism for this is, just a guess.
Experiencing an unusual taste in the mouth is common. I've heard of some people feeling a need to vacate their bowels when they are anticipating taking a drug.
So it's not at all surprising that when you actually take a drug you experience something right away, even before the drug has had time to work.
The mind is a powerful thing.
This is a completely untested hypothesis, but I wonder if these kinds of effects are somehow related to hallucinogen persisting perception disorder (HPPD). People experience some really powerful effects under the influence, and maybe the mind somehow learns to reproduce some of these effects on its own.
There have been times when the effect of coffee or marijauna hits me after a few sips/a bite of an edible, which feels placebo-y. But then I'm aware that it seems to be too fast, even as I start to feel it so fast, so could that still be a placebo effect?
I don't know, but it confuses me.