Yeah, the meme is simplistic for sure. What I get from it is that your true character is not what you cautiously do in public. Your true character is what you do when you're not in the public view and no longer putting up a façade.
It's unfortunate that this meme used the term "true test". It's not a true test. It's your true character. Your true character is acted out when you let your guard down, drop the façade and do what you would normally do free from the scrutiny of public eyes and the consequences thereof.
I think it is a really good meme, and can convey the tools to face a true test. I am sure as someone in a fiduciary position of trust, you've had the chance to do the wrong and the right thing where no one would probably know, and doing the wrong thing would give you advantage, yet you've done the right thing simply because it is right. It's when no one is watching that Character gets truly tested.
The message might be simple, but so are many in Freemasonry. As an oral teaching tradition, it is advantageous to make our complex messages simple. Like the simple words "Brotherhood", "Honour" and "Fraternity" , these are simple single words, but what is needed to discharge them as obligations can be complex and difficult but rather than have a thesis on these we use single words, but they are built upon by the whole system of our degree lessons.