It looks like the mi-8 had external fuel tanks installed. Thats the tank just behind the door gunner.

In this video you can see the tank on fire.

https://kyivindependent.com/fpv-drone-destroys-russian-mi-28n-helicopter-military-says/

And it was a PG-7M

https://militarnyi.com/en/articles/downing-of-russian-mi-8-by-predators-of-the-heights-details-from-the-unit-and-the-pilot/