21 minutes from wheel stop to passenger disembark. Were they serving pre-landing snack?
Within 4 minutes no living thing should be in that thin metal tube and only fire rescue professionals should be anywhere near that.
This is not a camp fire or barbecue to be safe once you hose it down by professionals.
Let me repeat one more time. Every day professional pilots order evacuations for minor fumes, smoke, tire burst and brake fires. Few pax get injured. So what, it is the right decision. It will be a shame to question them.