That said, it does not at all seem likely to me and I am fully into the typewriter theory. Berthold was not very common in the US and it would have been very expensive. But there were similar systems of US origin and I think other possibilities should be investigated, mentioned and explicitely ruled out. Even metal type must be considered!
Regarding the effort and costs:
During my apprenticeship as a fototype-setter on Berthold systems in the 80s, my girlfriend graduated from senior highschool with a thesis work about colorized photography (analogue of course ;-). I was very passionate about typesetting during my apprenticeship and my dedication was rewarded with free access to all tools, typesetting machines and even the expensive photo papers and film for private use as long as it was in my spare time. So I typesetted the thesis work of my gf on large A3 photopaper in a nice font on a Berthold ads 3000 and she would glue the hand-colorized photographs on it. The result looked better than any photobook you could buy at the time and it was way over top for the requirements of the thesis work.
So there is no reason to dismiss a possibility just on the assumption, that it would have been too expensive or too much of an effort. Sometimes it only requires a personal relation to make something seemingly impossible happen.