Here's a comparison between 125 and 400 ISO.
I pushed the 125 version one stop further than the 400 one, so they're equally bright when desaturated.
It's definitely a different noise structure, but I seriously don't know what to make of it.
125 does seem cleaner, and keep in mind that it's been pushed further than the 400 ISO side.
Looking at how good the 400 ISO version looks though, I wouldn't be surprised if it is indeed the camera's base ISO, but it does seem a bit high of an ISO for them to go with, on the other hand it could explain why this little sensor can do so well in low light. Also, if 400 ISO is in fact its base ISO, then they're doing a great job when pushing it to 125, much better than when pushing it to 200, which is somehow odd.
This article (and most others I found) also claims that the base ISO is 125.