GC usually (not always) works on separating by polarity. Chloroform (tricholoromethane) you mention has polarity vastly different from BA or methanol so it obviously would be separated from either of them.
https://sites.google.com/site/miller00828/in/solvent-polarity-table
I'm not saying that it's 100% the case, or that it was methanol... I'm just saying it's a possibility.... And that possibility sounds more likely to me than somebody doing 20% BA.
Shit, 4% make me limp for days.
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The other possibility is that CDNDA mixed up his solvents. A simple freeze test would be able to tell you if the BB in his possession is labelled correct, as BB freezes at 18*c.
If he is able to get his "BB" to say -5*c and have it stay liquid, it may be a mislabel and actually be BA (Freezing point of BA is -15*c)