Yea, 43 -> 45 minutes is a 5% decrease in performance, which sounds small but actually is pretty significant for any trained athlete. That's 15 seconds if you're running a 5:00 mile.

In cycling particularly you have all sorts of day-of considerations like hydration incl. electrolyte balances, RBC counts, sleep debt, glycogen levels etc. Even just having some carb-heavy meals a few days in a row would potentially affect his RPE. But none of that takes away from his deloading principle.