Sounds like you're suggesting they overcompensated, but I will not be so bold as to disregard a specification that explicitly says use 6AWG with a 50Amp breaker.
From the literatu

Rated Voltage & Frequency and Phase :208-230 / 1PH
Min./ Max. Operating Voltage :187 / 253 VAC
Circuit Breaker Size (A): 50
Min. Circuit Ampacity (A): 26
Wiring (Outdoor unit to Power Disconnect): 3C- 6 AWG (minimum)