Yes, I am also confused by this. Whenever we go through explanations of other videos, some answer choices are wrong because the topics discussed were never mentioned or we made an assumption. Why is this one different?

I would say that this isn't the best strategy. If you think about the SAT, this is a common way people eliminate answer choices. However, it's important to think about the LSAT separately from what usually works when answering questions. The stimulus is often an argument from someone and sometimes can contain opinions. This means that the correct answer choices will definitely contain absolutes in some questions since you have to go off of what is true in the stimulus.