How does the iPad expose its host name over the network?
The iPhone can be found by name using Bonjour. The name will be my-ipad.local
This name is the name in theIOS device with spaces and some punctuation removes as in @TheX's answer and then local as the domain telling devices to use Bonjour lookup. this name is not held in the router, Bonjour asks devices to call out their name on the network.