Hi Jackson
To me, a "column of men" suggests a line of men -- i.e. one in front of the other (not side by side). Thus:
1: columns of men five abreast = The columns consist of (long) lines of men, and there are 5 columns
2: columns of five men abreast = This seems to mean that the columns consist of 5 men (i.e. the each column is 5 men long) and the men are standing side by side.
Others may view this differently, but that's my take.