The two wooden buildings, located between the bank and the empty space next to the church, are not part of the bank. You can see they have their own signs above the front walls; we just can't see them from this angle.
If you look at a large bank, you'll see where the confusion over the bank comes in:
The clickable area which the game considers "the bank" is always the same size and shape, and that size and shape = the size and shape of the fully built bank. When the bank is smaller, you can click on some of the wooden buildings' roof area and it will treat that as a click on the bank -- but not because those buildings are part of the bank. It's only because the devs only created one clickable bank area, and it's always the same, and it overlaps those buildings some when the bank is smaller.
So, we do have 2 buildings there, plus the vacant lot between them and the church, plus the vacant lot between the sheriff and the mortician -- plus the space behind the mortician where the windmill now is. So really, we have a total of
five open spaces, and that isn't counting the expendable post building. Even with a fort (or whatever) taking up a slot, that's 4 new slots (plus potentially the post building) that are already in our towns which could be used somehow.
But this is all irrelevant anyway; the devs could just add a second screen of the town accessible by a click somewhere, and put a whole new slate of buildings there. So, it's a fun discussion, but kinda pointless IMO.