Working off Rich's excellent find, I relentlessly scoured the web until I came upon this variant, which seems to tie in both FIRST's clue and Dave's banana.
Kinda looks like the diamond plate 5 could be like the coin you drop into the water bottle on the fast-food counter, trying to hit a target - in this case the center of the field. No idea about the banana.
No real or imagined official GDC hints were harmed or knowingly revealed in the production of this red herring.