The big bang being an explosion is literally how we teach kid about the phenomena or how dictionnaries explain it:
The point is to make you understand that basic definitions that you find in your earlier year of studies or basic dictionnary definition are not necessarily correct with what the reality is. As in this case, the Big Bang being an explosion is not "valid", it's a missconception of the reality of the event which was an expansion of spacetime and the entire universe, like a balloon, suddenly big full of air.
The comparison here should have made you understand that your knowledge of gender should be refering to the reality of gender and not a random definition you found on the internet explaining you that there were only two genders.
If you close up reality to dictionnaries (which are not made to give you knowledge but to give you basic contextual information about a word) you will end up completely missing the material reality of existence.
Giving a definition to someone instead of an argumentation, is a proof that we don't understand the essence of the concept and need to rely on a basic, restraining one sentence contextual definition to counter it. And it's often a bad definition.
As for the universe, there is no problem, you not understanding that knowledge does not have an impact on the word,
but you refusing to question a basic definition you learned when you were a kid can have massive consequences for trans people if you hurt them.