Popper
Popper
[Miss Lenhart is teaching a class of three students; Hairy, Ponytail, and Science Girl, sitting behind their desks.] Miss Lenhart: There's no evidence that Karl Popper wasn't born on July 28th, 1902. Miss Lenhart: No one has proven that he didn't grow up in Vienna...

In this comic, Miss Lenhart teaches to a class comprising of Hairy , Ponytail , and Science Girl about Karl Popper . Karl Popper was a philosopher of science who endorsed the idea that science is distinguished from non-science by treating its theories as falsifiable. This means that science does not treat any theory as definitive, because future research could show that it is false.
A not uncommon reading of Popper assumes that instead of proving hypotheses, scientists are disproving hypotheses. This reading leads to technicalities like the ones stated in the comic: Instead of asserting that Popper was indeed born on July 28, 1902, and grew up in Vienna, a scientist can only assert that there is no evidence disproving these facts, which seems counter-intuitive because one cannot disprove the facts of Popper's birthdate and childhood residence.
Note however that falsifiability is often interpreted to mean that there has to be a way to disprove a given statement if it is wrong, or to distinguish between two mutually competing hypotheses; not that a statement is accepted solely due to the lack of evidence to the contrary, e.g. a birth certificate is often used to establish a date of birth and falsifying that date of birth would then mean calling into question the birth certificate's authenticity or accuracy, but without any historical records of the date of birth one would normally not even speculate at all about the precise date of birth.  As such reasoning solely on the absence of proof to the contrary would be considered unusual in most contexts.
The humor comes when the comic applies this idea to the life and biographical information of Karl Popper himself. Note that in real life, such a subject would be a matter for historical proof, not scientific, and would thus fall outside the realm of study Popper was thinking of.
The title text takes this reading a couple of steps further in a kind of meta-analysis. It points out that Miss Lenhart 's claim of no evidence has not been proven false, and also that we're dealing with only the knowledge of a single individual who may not be aware of evidence that might exist.
Another reading of Popper points out that Popper’s philosophy discarded proofs altogether as a defining feature of science. Thus there is no such thing as definitive evidence in Popper’s notion of science: Even falsifying assertions themselves are seen as falsifiable.
[Miss Lenhart is teaching a class of three students; Hairy, Ponytail, and Science Girl, sitting behind their desks.] Miss Lenhart: There's no evidence that Karl Popper wasn't born on July 28th, 1902. Miss Lenhart: No one has proven that he didn't grow up in Vienna...
