It does, indeed, show that going out exposes you, but not to the virus, as agar can only grow bacteria.

The overall point of the meme is that being out and living life means that there will always be a risk of infection from something, be it China Virus, regular flu, or even some kind of bacterial infection. Hell, we have a form of staph on our skin that, should it actually manage to infect us, will kill us (which is why whenever you get a shot, the nurse sterilizes the area with alcohol)!

Being an adult means that one accepts the risk of going out, and if one is really that scared, then that one needs to stay home and let the rest of us live our lives.