What it means to say humans are 50% bananas and 98% chimpanzee is that us humans share many of the fundamental, "housekeeping" genes with bananas like cell growth and respiration as well as a vast majority of our protein coding genes with chimps.
Chimps are us humans close relatives, which highlights a shared ancestry but using different metrics for comparison and not identical DNA sequences.
The chimp comparison to humans is about gene similarity and coding regions, while the banana comparison to humans focuses on having a comparable gene for basic cell functions "orthologs" rather than identical DNA sequences that show life's common building blocks,
For the 98% chimpanzee similarity to humans, chimpanzees are us humans closest living relatives, which share a relatively recent common ancestor around 6 million years ago.
This high percentage of similarity of chimpanzees to humans reflects that the actual DNA sequences in our genes and non coding DNA are very similar, which leads to nearly identical proteins and traits.
For the 50% banana similarity to humans.
Humans and bananas also share an ancient common ancestor from over a billion years ago, which makes them also very distant relatives.
This also refers to having homologous, "related" genes which perform basic, essential functions for eukaryotic "complex" cells, like producing energy or building cell structures.
And it's not about 50% of our DNA sequence being identical, but instead it's about having a version of the same gene "an ortholog" for basic functions, even if the DNA code for that gene is quite different.
The numbers are also not comparable directly because they also measure different things, such as the chip stat is about the close genetic sequence similarity, while the banana stat is about sharing the basic gene functions "orthologs" for the universal cellular processes.