I don't see no math but what the note says in your picture is correct.
Here's the thing about solar panels (and my numbers are just for ease of understanding):
If a panel is constructed on 24 "1 volt" plates to provide a 24 VDC output, all it takes is a slice of shade to cover just one of those plates and your output will essentially go to zero as that shaded plate acts as an open.
So your pic showing 2 panels in series, in parallel with another 2 panels in series, is more reliable as far as always providing some charging even when some panels may be partially shaded.
Ted & Melinda
2016 ACE 27.1
2016 Chevy Sonic Toad
2020 Chevy Colorado Z71 Trail Runner Alternate Toad