In looking at the internal footage a few notable observations are apparent
1, sooting on the panel junction in front of the exhaust outlet, and 2 fire under the wing - which is definitely abnormal and extremely alarming.
It would be a presumption that a fire has broken out, at some stage, either between the engine power section firewall and nacelle firewall, or a mechanical failure has occurred with the engine power section(Cylinder or multiples of, or rotating elements) and an uncontrolled oil leak is igniting on the exhaust and exiting vial the cowl flaps - which there would be no fire suppressant for(reserved for the Accessories section - oil and Fuel services etc).
In the departure video there is clear flaming in the exit area of the augmenter, which indicated something mechanical is amiss in there, the popping of the engine, smoke and strobe effect of the video indicates RPM changes occurring, and waiting for the Governer to assert itself - rpm recovery. Im going to assume the later - if you have a fire in the accessory section, fire alarms would sound, the engine(if determined is overheating/or on fire) would be secured and extinguishers used - Securing of would cut fuel and oil supplies and stop pumps for doing just that - The propwould also be feathered and stopping rotation.
A failure in the Power section may produce a fire that cant be seen, and if still producing power may lead you to continue until safe to secure. As for landing in a paddock - there are two pilots who will know the events relating to those decisions. Mine is but speculation, I am willing to speculate that they may have been made aware of an external fire late in to the flight and decided being on the ground in a controlled fashion was a better outcome. than pushing on to the runway.