That router lists Mac requirements in its installation guide online, a good sign that they have considered and tried to accommodate Macs. It seems likely they can pass AppleTalk packets.
When you add a printer, you should be deliberately selecting AppleTalk as the connection method. [Try deleting the old printer and recognizing it anew, just to be sure.]
The printer may respond with its name under other protocols. It contains an HP printer emulator, so it may respond with its name, expecting that you want to print in HP PCL protocol. It may also respond to LPR/LPD, but it is not actually capable of printing that way.