Nope. I have it from good a good source he did it himself. I seem
to remember that the old assembler version had build in constructs
for headers and footers and which got radically removed in the
C-version. That one gave you the famous trap mechanism etc. Although
the basic structure of the assembler version starts out the same
it quickly deviates, so it cannot have been turned from as into C.
The N/TROFF manual describing the C version stems from 1977.
Wikipedia dates the rewrite into C from 1975
I seem to remember that there where actually two versions of Edition
6 unix. The second one came with typesetter C but my memory is
foggy about these details.
jaap