Mathieu S. received a "Collection" badge on Sep 15 because they posted something that people are adding to. That's harder than it sounds - usually people are just like, "meh," (which, and I get that we're now waaaaaaay off topic, is a really annoying thing to say under almost any circumstances).
Mathieu S. received a First badge on Sep 15 because they were the first person to post a thing even though maybe someone else posted that thing after them and got featured for no other reason than, like, sometimes a bunch of people post a thing and the first person to post the thing doesn't get the credit that they deserve. But now they are getting the credit! This is the credit!