I recently replaced a couple of my own Denon receivers and noticed the same thing. I have a 4x4 matrix and both receivers showed up with the same label after powering up. Both were connected to the same DirecTV Genie. I’m not 100% sure, but it appears they read data from HDMI (EDID, maybe?) and automagically renamed themselves. Either that or Denon has a database and changes the name. The receivers also changed the Game input name to Xbox when I connected Xboxes.

You can change them back to the standard name in the Input menu.