First, no reason to be sorry, your question is not silly at all...
It is no related with AirPrint but with the network connection itself.
I afraid the only solution is to connect your iPad to the 2.4GHz network as the HP device uses:
A device operating at 802.11n 2.4GHz, cannot connect to another device operating at 802.11n 5.0GHz.
As you may find listed below, the HP device use 2.4GHz only:
Not all devices that support 802.11n support both frequency bands. So you can't connect a device that uses 802.11n 2.4GHz to a wireless router set to operate at 802.11n 5.0GHz only. All HP printers that support 802.11n use 2.4GHz only.