It is not unheard of, RFMO, I don't think there is anything to worry about. Since your hubby is scheduled for an interview, they might be confirming that they are able to contact him (in case of anything on the interview day or before in case there is a change of date). Additionally, confirming your information allows them to establish that he is aware of your side of the information provided on the application (this is a good thing that he was able to provide that for them).
I would encourage you to go ahead and send the email about your concerns. Why? Because it leaves a paper trail. When dealing with government offices, you always want to document any actions that cause concern or seem out of the ordinary way of doing things. Simply explain that having provided all relevant information on the application, you were surprised and concerned that they needed to contact your husband to provide them again but you hope that everything provided was adequate. You are both happy to assist them in future if there is anything else that arises, and thank them for letting him know you could send the email to them. (You want to keep it concerned but non-adversarial, hence the offer to continue to assist them if they need anything else, and politely thanking them for "letting" you email them about it.)