Looks like they just wrapped the strand wire around the copper and shoved it in there. No trace of a wire nut electrical tape or other connectors. Crazy thing is all other connections look emphasis on look like the time was taken to do it right. So why just skip over one connection?
There have been a lot of these failures written about recently. Supposedly they have come out with a new style transfer switch that allows the #10 solid conductors to be landed on terminals to eliminate the need for these splices that have failed on many rigs. Because these circuits are often running full capacity @ 30 amps for hours and hours, they must make 100% contact. Half ass splices will overheat and fail.