welcome to HCM!
I have gone through your query and from my clinical experince I can say that keeping in mind the normal BP of your husband- 130/80 , the reading of 115/47 is actually low, more over there was associated weakness, which almost rules out that it was a machine error.
Had I been at your place, I would take him to a doctor, preferably a cardiologist, and get his BP, ECG, done to rule out any cause for the same.
It will also be good that you get his routine blood tests done- blood counts, lipid profile
, sugar levels, liver
function test, and thyroid
there is a problem which occurred only once, so please donot worry much, but do see a doctor and get him examined.
Hope the reply is helpful
Feel free to ask more questions.
Dr. Manisha Gopal