There is no way in the world a circumcision on a new born would be done without having the parents sign a consent. It's after all a surgical procedure.
We're talking 1950s and a non US mother. In just about every country, non citizens and immigrants are treated with less regard and differences of opinions or customs are usually settled to the advantage of the customs of the host country.
Perhaps the hospital had an all-in procedure for births that 'naturally' at that time included routine circumcision as normal. Perhaps it was even mentioned in the release forms that few read in their entirety anyway. Perhaps no one bothered to make any changes to the release forms or whatever paperwork was required. Perhaps it was the natural and unquestioned assumption back in the 1950s that male babies were always of course circumcised, with no doubt about the matter. Perhaps no one cared about the wishes of a foreign mother.
In any case, I heard about this from my teens till my 60s and it was not something my mother ever forgot.
If you've never been an immigrant or foreigner living in another country, it's difficult to understand how often they are treated as being slightly under par on so many levels, how little is often taken into account of their wishes. Nor is it only because of language difficulties either, because my mother could pass for a native speaker, as her father grew up in Great Britain and taught her (and me) English.
I've been sometimes treated as a foreigner in the US, then afterwards as an American in Belgium and now as a northerner in Spain ... once it starts it never seems to end ... there is always something you're doing wrong ... ha ha.
So I'm pretty certain that as Jimmyt44 remarked, he was not far off the mark.