Hi Moufflon, I don't know why no-one has replied to you!?
With a wheel/ wheel-well fire, or indeed any other kind of essentially external fire (engine, APU), the first priority is to get (or keep!) the aircraft on the ground. After that, unless you are 110% sure that the fire is TOTALLY extinguished, an evacuation is a serious consideration. Even if ground emergency services are on the way to the aircraft, an unextinguished fire can very quickly become a conflagration, killing all on board.
There is no way (apart from a VERY few airliners) to view the gear area from the flight deck. So you have no way of knowing what is happening down there, apart from possibly a faraway ATC controller or a ground rescue vehicle on his way to the aircraft. Further, even though all may look quiet, the metal of the wheels is rapidly increasing in temperature (due to dissapating energy from the brakes), and any fuel leak may be invisible. Next thing, temp reaches flashpoint and, instant inferno. Lastly, of course, there is no guarantee that the fire services will be able to extinguish the fire before the aircraft and its contents are destroyed.
Regarding pax evacuating too soon, normally the problem is getting them out fast enough! Provided things go 'as planned' (caveat intended), no action will be taken regarding evacuation until a command is received from the flight deck. If the FD is disabled or uncontactable, some airlines allow the cabin crew to initiate evacuation. (In an Airbus, there is a switch in the roof that sets the evacuation possibilities to either 'Captain' or 'Captain and Purser', depending on the airlines procedures). An inherent danger in the latter is blowing slides into running engines, but an emergency is just that, and often improvisation or lateral thinking is required. Bear in mind that fear and panic amongst the pax are an unfortunate but very real part of any abnormal procedure.
Ironically, most injuries are usually sustained as a result of the evacuation, not the emergency! But IF you leave the pax on board, and IF the aircraft does burn out.....
Not an easy call.
My opinion; in this case the captain did exactly the right thing by evacuating as soon as possible. Well done!!!