Going a little further with nos’s comments, I turned up a scanned version of the GE-635 Programming Manual, and found the following in the section on the macro assembler:
The GE-625/635 Macro Assembler is
being provided to give the
professional programmers some of the
conveniences of a compiler and the
flexibility of an Assembler. […] The
output options enable him to obtain
binary text in relocatable as well as
absolute formats.
So, it appears that the use of “binary text” was a GE colloquialism, or perhaps a commonly used term at the time (remember that those were the days when card readers/punches were used for much IO). So, one possible path is GE, to Multics via GE-645, to Unix via Bell Labs’ work on Multics, to Linux.