Ok. I have to disagree though that this means that he couldn't possibly have heard of PRs before. That he must be able to recognize them if he has heard of them is just an assumption.
But come on, we're not talking about novelists or diplomats or other minor celebrities that people may have heard of without seeing. We're talking about groups of people that, over the past 20 years, have had weekly, extremely public battles with giant monsters bent on destroying the world. The human race owes its very continued existence to the Power Rangers dozens of times over. They'd be world-famous, revered figures. And they all have a distinctive, formulaic, and very flamboyant appearance that would surely loom very large in the public's image of them. And if these characters are high school students, that makes them under 18, which means there has never been a time in their entire lives that the Power Rangers have not been an integral part of the world they inhabited. So hell yes, they should absolutely know what Power Rangers look like.