Open them in different orders. Click outside, press Escape, and watch the list of open popovers.
Open one, then the other: the first closes. Click anywhere outside, or press Escape, and the open one closes. That is light dismiss.
This one stays open through clicks outside, Escape, and other popovers opening. Only its buttons close it.
Open the Trail menu above, then press Tab until this section's "What is a hint?" button has focus, and press Enter. (A mouse click on it would count as a click outside the menu, and light dismiss would close the menu first.) Where popover="hint" is supported, the menu stays open beside the hint, Escape closes the hint first, and opening an auto popover closes the hint. Where it is not, the value falls back to manual: the hint ignores Escape and clicks outside, and stays until you press its button again.
A hint is for passing information, like a tooltip. Opening it leaves an open auto popover alone.