TIOBE is meaningless - it is just search engine result numbers, which for many search engines are likely a wildly inaccurate estimate of how many results match in their index. Many of those matches will not be about the relevant language, and the numbers probably have very little correlation to who uses it (especially for languages that are single letter, include punctuation in the name, or are a common English word).
54 kg of fentanyl is an insane amount to have all in one place.
Just to put it in perspective:
I’m not sure why they’d stockpile so much in one place, given they apparently have the capacity to manufacture more - unless they were planning to use it to kill people (see: they also had a weapons cache and explosives) instead of to sell as a drug. Or perhaps the 54 kg is an exaggeration and includes packaging and so on.