It's all too easy to be wise after the event. Do we know whether smoke/fire warning was still annunciated in the cockpit after landing? If so, it would be a no brainer for most of us. Stop, shut down and evacuate right there on the runway.
But, if the warnings had ceased? Test the warning system - yes we should do this after any fire warning has extinguished (but it is surprising how many QRHs don't specify this). So, the system tests normal, no cockpit indication of fire or smoke now. Maybe some residual smell (could be expected after such an event). Now what?
RFF say it's under control, now what?
Company 'culture' and prior training may also be at play. If they are super critical of pilots who chuck pax down slides to the delight of the gathered media, maybe that would explain why they were so keen to make it all appear 'normal'.
Not defending and not applauding; merely playing devil's advocate.