No this was just added for some projects that wanted to integrate Mochi into their website. E.g. if you have a website / platform that provides learning material and you'd like to seamlessly integrate spaced repetition reviews without having your users leave the site, you can embed Mochi and let them review cards right on the site.
The feature will likely be expanded in the future to allow for more embedding options.
Is this done using the API thing?
This isn't related to the API at all.
Does this allow sharing your decks with others?
In a way, yes, but you can also share decks with others by sending them the share link.
I was wondering if it was possible to share a read-only replica of a deck (with all the UI's, reference links, etc)
Unfortunately no, that's not really possible right now. I have plans to expand the sharing system to include things like this, though.
Thanks for the reply, Matt. If I may, what's a "share link"? Where do I find it?