You make a great point, but the purpose of this lesson is to hone your skills for understanding the placement of necessary and sufficient conditions within particular phrasings of sentences.
Wherever introduces the sufficient condition, so we know "smoke" is the sufficient condition, and that means fire is in the necessary condition.
Smoke - >Fire
Sure, there do exist examples of smoke without fire, but this is just an example that was used for fun. When you're answering questions on the LSAT, you always want to assume the premises are true. Questions on the LSAT are always testing your ability to identify the argument structure and flaws that exist within said structure (that is, flaws occur between the premises and conclusions of the argument).
I can tell that you're reading things carefully, and that's awesome. Keep up the good work!
