I realize now

intelligence is relative.

There's missing the joke, and there's this.

Perhaps. Or perhaps the joke missed the mark? These silly observations require a few things. One such requirement is that in order to work the observation must posses a humorous insight. In this case the implication is that earth is full of morons, except of course the reader, and the teller, because they are smart enough to know everyone is a moron. Much like the online IQ tests that say things like: "only 2/10 people get this question right.." then ask you what 4+4 is or some basic thing- most people will obviously get this and this be "one of the smart ones." The idea is that people will feel like "yew haw he'll yeah. I'm smart surrounded by idiots." One might call this pandering. Now see that it combines a sort of "dad joke" cheesey humor with the cynicism to imply earth is full of morons (I"intelligent life" is a sad joke pun, and "everyone but you is dumb" is a cynics stance) two things which can combine if done well but rarely do. So it has been met with cynic humor you missed.