This might sound like a strange question but...
S.M.S.L is telling on the Homepage that this amp does have an balanced output. Based on your measurements, it doesn't.
So it should be totally safe to sue them right? They are stating false claims on their official homepage. Did that happen? Or does just no one care?
Based on what measurements? Amir's did not prove the output was not "balanced", though he may be right, that it wasn't truly balanced by the common definitions.
In order to be sure, one needs to see the schematics, or take other measurements than just the output voltage that is just one indicator. The lower than expected output could have been by design, for other reasons.
I would think the quickest way to find out, is to email smsl.