That's the first time i've seen thick black smoke coming out of their chimney. Usually it's an off-white tending towards battleship grey. (And no, I do not hang out there waiting to see smoke from their stack, but I know where it is and travel near there fairly often.)
My guess is that the "afterburner" was overwhelmed and ignited particles were lifted past it to land on the roof. The addition of an "afterburner" and a fly-catcher makes cremation much more acceptable in locations that are not way out in the country.
Someone on the fire department that responded told me that it was a "good thing" the rubberized roof caught fire, as that masked the odor of the burning fat. It's not shown in the video but there is a McDonalds just a block away. The thought of Mickey D's vented fat and that from the crematorium mixing in the neighborhood is almost too much for even my imagination.
stay safe.
