Why might a man of 65 yrs have a blood test that would normally be offered to a pregnant woman to check for abnormalities to the baby?

It might be very common for a 65 year old man to have his hormones checked, as men have big changes around that age pretty much as women do. Also men and women share many of the same hormones, just in different concentrations. But I'm not aware of hormone tests that would reveal genetic abnormalities? There are other blood tests to check for them, and men do contribute half the chromosomes (I can't tell if you are asking about a soon to be father or what).

Hormone tests are not just for women, and since you did not specify which test by name and what they were checking for.
But I guess if you want to know ask him and if he wants you to know he will tell you.