The oil level drops below the oil window when the engine is running, so any emulsified oil will gather in the window.
Hence why it now looks like it does.
Left for another 5 minutes and you wouldn't have any melted plastic left to look at, and no need for this pointless rambling cluedo type of discussion.
its a melted sightglass . someone has left it running too long . DAMHIK . .
Mine eventually melted and burst spraying everything in my garage with oil .
replace the glass and change the oil it'll be fine . I've done 20000 mile since with no mechanical engine related problems
Fill the sump with yobbo brand cheap oil and ride it for 100 miles to flush out all the crap. Then change the oil for some decent stuff. Change the filter too.