I'd really like to understand this deeper: are you sure your macbook was hibernating, even if it was closed? Are you sure the proximity advertisement came from the laptop? Usually it is the iPhone doing it.
I've seen that in airports and malls, more than 90% of the advertisements around are iPhones (Android doesn't do BtLe advertisement) and Windows computers (from the shops and stores). A small minority are beacons and wearables (iWatch, Fitbit, etc.) In libraries sometimes I can see Macbooks, but they all are non-hibernating.
My headphones are only paired with my macbook and my android phone. I always am walking with the headphones paired with my phone, so that's one of the two devices. The only other device is my macbook pro, that is often sitting on the kitchen table with it's lid closed, and unused for several days, and yet this happens every day. I obviously don't know what exactly is going on, but if they can "connect" then presumably something about the bluetooth is still functioning.
If you left the MacBook connected to the power supply and it is a 2016 model or later then it likely isn't really hibernating, even with the lid closed. By default, most of them remain active when connected to power.
However, you can disable the Bluetooth connection. Go to System Preferences > Bluetooth > Advanced Button and deselect "Allow Bluetooth devices to wake this computer."
I wonder who does the advertisements here. In BtLe the standard is to have the Peripheral (i.e: the headphones) doing proximity advertising and the Central doing the scanning. But, in principle, anything is possible.
I've seen that in airports and malls, more than 90% of the advertisements around are iPhones (Android doesn't do BtLe advertisement) and Windows computers (from the shops and stores). A small minority are beacons and wearables (iWatch, Fitbit, etc.) In libraries sometimes I can see Macbooks, but they all are non-hibernating.