Is not so simple, there are TWO grapefruits. One is an hybrid, the other is one of the four fantastic ancient Citrus species, that are the grand-grand-grand-parents of (almost) every known fruit from that family. "Everything", from Uglyfruits to Blood Oranges to Key limes is an hybrid except a very few wild species
Um, I see what are you saying, this part of the diagram with orange being older than pomelo is clearly wrong. Good point. Is good to remind that genetic analysis must be interpreted wisely together with other facts, or can easily mislead.
In general this view doesn't do a good job of explaining citrus fruits. There are a huge variety of hybrids mostly deriving from combinations of the mandarin, pomelo, citron, and micrantha (lime).
This diagram (on the Wikipedia article for Citrus) gives more information: https://en.wikipedia.org/wiki/File:Hybrid_origins_of_Citrus....