Well, they planned to use 'burners' for this eventuality, which was revealed through the recordings and usage was verified by Sheriff. We know that some of the officers got really excited and verbally stated their desire or issued a command to, 'burn it down.' The cabin has burned down. Sheriff uses plausible deniability.
Why would they need to use a pyrotechnic one after using a cold one? If the first didn't flush him out then he obviously had a gas mask, so the second wouldn't work either.