Link Layer Devices & Protocols - Study Guide question

I’m going through all the study guides and there was something in the Link Layer Devices and Protocols study guide that didn’t make sense to me…just wondering if it’s a typo, or something else that I’m just not “getting”.

On slide 38 of the study guide (2.4.5.5 - Forwarding Tables), the second bullet point says, “In our example interface, 4 has no hosts attached.”

Can anyone help me make sense of what is trying to be said here? TIA!