I'm not 100% sure which is why I posted the raw numbers first.
I believe they are calculating the offensive and defensive efficiency of the lineups you play against and averaging them out. It makes sense for a guy like Boogie Fland who played mostly against non conference teams, and then his team played the majority of their SEC schedule without him. His On/Off looks amazing, but the adjusted On/Off looks closer to what you would expect. For a guy like Tre Johnson, who was healthy the whole year, I don't understand how the level of competition he faces was so much more difficult with him on the court than with him off the court.
They calculate a weighted average based on the lineups played against. Tre played nearly every minute except during games against weaker opponents, so the strength of schedule (SOS) for the minutes he actually played is very high. In contrast, the SOS during the minutes he sat is much lower, since those minutes mostly came against weaker competition. The analysis is granular to the minute level, not just at the game level.