A poser is someone who belongs outside your little universe who likes and is interested on the same thing you like.
You’re a scientist. Intellectual. Reasonable. Logical. You studied a particular thesis but somehow your results always negate your hypothesis. Here comes a non-scientist man. Street smart. Bully. A jerk. The kind of guy who used to bully you in high school. Somehow he accidentally stumbled upon the problem you’ve been studying for years but he managed to find a solution amd went famous for it. Got tv interviews etc. You call him a poser for acting more than who you thought he is.
In reality though, he’s really smart but because he is outside your little science circle, you figure him for a poser.
You’re an ordinary Joe in an ordinary town. Blue collar. Street smart but don’t read much. And you drink Tuba (a hard drink made from coconut aka palm wine). You claimed Tuba as yours and something that belongs to your people. Then you found out about these rich kids in the neighboring town who also enjoyed Tuba. They don’t only enjoyed it, they pretty much nerd themselves around it, reading literature about Tuba and formed a society based on their love of Tuba. They’re the kind of people you despised simply because they belong to the upper class and you have your own biases towards that social class. So you call them a poser.
In reality, they really are genuine on their love of Tuba but you don’t see them that way because they’re outside your little social circle.