Yeah, I'm pretty sure it's different. This is a new and previously unannounced animation project, but no details on what it is exactly. Could be a movie, an OVA series, another season, or a spin off thing.
Overlord S2 is in production. It was announced during the second compilation movie premier. Given that it had two compilation movies and new artwork, it wasn't much of a surprise to hear that they were doing a second season.
There's no official date for it yet.
It could be as soon as the upcoming fall season, but my guess is winter or spring.
DxD is in the exact same situation. S4 has been announced, but has no official release date yet.
There are a lot of shows that have this status right now. Non Non Byori, New Game, Fairy Tail, etc...
It's not unusual, outside of a few special cases that have their own press events, most shows get a release date when the next season schedule gets released, which is usually about the halfway point of the current season.