It feels like they wanted to make sure that no one distributes a modified "Winamp" that isn't built from the official sources, which makes sense, but they went too restrictive on it. The usual way to go about it is to say "if you want to maintain and distribute your own fork of this product, you must change the name and the logo to make sure it doesn't infringe on our branding". Telegram does this for its client apps, for example.
I bet that they would disagree with you. This is an "all rights reserved" "source available" license. Given the redistribution restrictions, their assertion that it is a "copyleft" license is clearly false.
