The caller ID was just the phone number "5302310359" so I answered and instead of hearing some prerecorded pitch, I heard the "your request to be removed from our list has been processed" message before the line disconnected.

I know not to press any prompts etc on these calls and use a headset at work where I wouldn't bump buttons accidentally. My guess is either a new system that is not fully set up, or maybe the owner of this number pissed off some scammer who is masking their number with this one to frustrate the real owner.