Well the old station channels corresponded to an actual frequency i.e. ch 4 was the same frequency everywhere.
On over the air you have ch4-1, 4-2, ect but they aren't on any specific frequency, it's a VHF channel on the old system on ATSC it's what ever frequency the FCC assigns and likely a UHF frequency. Your TV treats the old channel number like the call sign. (WGBH) Basically makes the transition easier for people ch4 is still displayed as ch 4.x (up to 4 sub channels)
Sorry if this is confusing, it's only because it is.
Scary part is it makes sense to me.
To put it briefly the TV doesn't know where ch4 got parked on the new band so on initial setup it scans the whole frequency band. Neat thing is they can re-assign a channel and the info is transmitted to your TV automatically. Your guide will load channels that you can't tune in though. (mine does) Where I'm at it shows channels from Gainsville, FL. because some people are in an over lap area and can pick up both cities. I can't and my TV doesn't know it's actual location. (Sat receivers ask for your zip code)
BTW the antenna your using a lot of people think the "front" is the arrow pattern (the longer VHF rods) it's actually the stubby UHF three prong portion. (short rods) The two offshoots are actually reflectors to the center section. (don't ask, some guy with a lot more grey matter than me designed it)