What makes that the more likely scenario?

Because it's their facility

this facility has never had this issue until the FBI showed up to commandeer their incinerator.

Says who?

For all we know they've had issues everytime they incinerate but they ignored it cuz a lil bit of smoke from 1 cat is way easier to shrug off compared to a huge amount of meth

It's very possible they just have been ignoring the problem because normal smoke from incineration a very small cadaver isn't a big deal, whereas meth fumes are extremely toxic and not something you can just shrug off

Lord knows I've worked with workers who have the "I've been doing it this way for 10 years and never had an issue, don't be a pussy" type of attitude too

So hard to say, without more info it's basically just us speculating.