Sorry for the late reply. Book deadline!
First off, like I said, women can have toe orgasms. The brain can do wonders.
Second, your womb is your cervix. The clitoral network contains thousands of nerves that extend deep into your vagina and around your cervix. So what you are feeling is the clitoral network activating those nerves. Btw, it can also innervate the vagus nerve.
more here: https://carlynbeccia.substack.com/p/is-stimulating-the-vagus-nerve-the
Not all orgasms will feel the same, and every woman’s network of nerves differs. In studies, most women report that stimulation of the glans clitoris (the outside nub) feels sharp and quick, while stimulation to the deeper nerves feels long and rolling (similar to how you described. Btw, I experience the same.)
More on that here: https://carlynbeccia.substack.com/p/most-men-and-women-dont-know-the
Think of the clitoral network as the start of a super highway that activates other super highways. But without the brain and the clitoris on board, you are not going anywhere. In other words, if I ripped out your entire clitoral network (which would be tough because those nerves are spindly,) you wouldn't feel what you are feeling.