I also received a notification that my Android Blue Iris app was using my microphone in the background, even though I did not initiate use of that feature.
have you emailed support?
if it was a hikvision app reporting back to china there would be cause for concern. Do you think the blue iris app is spying on you? if so, I suggest you delete the app as well as the server software because that could not only be passing audio but all your video as well.