It’s the core BLE integration. It supports discovery.
I only added a BLE proxy last week, so am no expert but this is what I found:
I used the third party Bermuda BLE Trilateration integration to add my three garbage bin BLE beacons. Even though I am not actually room tracking this works exceptionally well to tell if my bins are in the drive or on the curb. I no longer get reminders to put the bins out if I have already done so as I can use the distances as a condition.
However, not long after adding these trackers I got the same discovered tracker you did shown above from the core BLE integration. I added one, it was a duplicate of my device already tracked by Bermuda and I saw no benefit to what I already had so I deleted and ignored the discovered devices from the core integration.
What you are seeing may be an ibeacon BLE broadcast that was received (even if only once) by your BLE proxy. Could be someone walking past your house.
My proxy is too far back from the street to have this happen but I do this in Bermuda anyway:
There may be a way to do this for the core BLE integration too.