The audio file wpn_stuartmaingun_mn located in the folder stuart suggests the Stuart was either planned and cut sometime in development, or its resources were borrowed from other games for use as placeholders.
The subtitles in The Desert Fox mistake the Stuart as the M4 Sherman.
The model in use in Big Red One is the M3A1 Stuart, the predecessor to the M5 and used during the North African campaigns. The game model also features markings and insignia appropriate to the campaign and period.
The M3A1 Stuart in fact has locations for up to 5 machine guns, but the anti-aircraft top gun mounting was not used and the dual side sponsons appear to be closed up.