The open-source licenses that I’ve used don’t require surrendering copyright.
The creator doesn't "surrender" their copyright, but someone can fork it and then have ownership of their version. "Winamp will remain the owner of the software" indicates you won't have ownership of a fork.
Again, it doesn't clearly state whether it will be "FOSS" or "Source Available", but if they were planning to go FOSS, you'd expect them to say something to make that clear. Leaving it vague seems like a strategy to get attention while not actually lying.