From the article:
The third volume will feature nine animated shorts from nine animation studios in Japan. Returning studios from the first volume include Kamikaze Douga, Kinema Citrus, Production I.G and Trigger. New studios for Volume 3 are ANIMA (in co-production with Kamikaze Douga), david production, Polygon Pictures, Project Studio Q, and Wit Studio.
There was a Volume 2! The main difference is that it featured animation studios from elsewhere around the globe instead of Japan. So, it isn’t included on sites like MAL or AniList. Similar to the first season, it has some episodes that are better than others, but I generally prefer the first season between the two.