Re 1) xxx_diffMesh.txt is not an output of the statistics, but is for general information. It is always the difference between 2 groups for whichever group variable is present. If there is no group variable, it may still get written out (and would be all zero). In your case, simply disregard.

Re 2) The terminal output during reading of the mesh/feature files shows the name, followed by the group label (which is not important for your interaction analysis) and the scaling variable. Since there is no scaling column in your test, that information is basically random, so just disregard that output.

Martin