It is certainly a double standard but which is justified in a certain way.
It is normal that the mothers who take care of their son, who were bathing them when they were still unable to do it themselves correctly can be present for a medical examination of the boys, a few years after she stopped bathing them, at least until they reached puberty.
After, as I said previously, I think that the mother may also be present for the examination of a male teenager, above all if he is not very mature which is often the case for boys, but she must be more discreet.
Some teenagers can even feel more comfortable in a doctor office if their mother is still present as far as they are not exposed naked in her plain view.
Nevertheless, it is not fair if the doctor is performing a genital exam right in front of her eyes but of course, if there is an issue, she is very much concerned and can watch while the doctor explains what it is.
I believe that the men who complain about this double standard are too much thinking to their embarrassment and not enough to the necessity for a mother to know of her son is in good health. It is a normal interest, without anything unsane.
As one has previously said, we, men, will not be here if there was not a women to give us birth, a mother is generally the person who knows best her son, even her body until he became an adult.