Ah, thanks for that.

For those reading: after you select a collection, there is a small "i" icon at the top of the screen, near the search bar. Clicking it gives a link to the source and license info!

----

Though as others have mentioned: beware that there is still obviously-trademarked stuff in there; check the source to be sure. If you're looking at a specific icon, there doesn't seem to be an obvious way to get back to the collection it came from (and thus see the original license terms).

The availability of trademarked icons (such as Google and Amazon, linked by others) makes me think they just crawled for SVG icons and slapped an OFL on them, which you can't do.