Chrome in full screen weird behavior when pressing option + command + M
Yeah it's a visual bug. Option + Command + M is a shortcut to minimise all the windows of the frontmost app to the Dock.

However, you should not be able to minimise windows which have been put in full screen mode. Most apps will simply not respond to the minimise shortcut if they are in full screen, but Chrome will go black.

You can restore the windows by clicking on the Chrome tab in the Dock.