Well, his painting shares some superficial features that look similar to that one photo. Like a similar overall shading from light to dark. Other photos of Pluto look nothing like Dixon's painting. The "Pluto with a Heart" pic, for example.
Dixon's painting is cool, but let's not make it something it's not.
Let's also remember the fallacy of multiple endpoints. Many artists have rendered visual guesses at what Pluto might look like. And many will be totally wrong. We're cherry-picking the best example in Dixon, not a typical one.
Great point (love the fallacy of multiple endpoints).
But there also may be some "algorithmic" smarts here in terms of Dixon's interpolation/extrapolation of what cold planetary bodies look like, even with what was known in 1979. Think of an image-generator bot that took some parameters of what was known (distance from Sun, whether it was a gas planet, atmospheric conditions, position relative to the asteroid belt, how size affects features) and kicked out plausible planets. This might be close to what you'd come up with if you made the mistake of forecasting more meteoric impact than actually occurred.
Dixon's painting is cool, but let's not make it something it's not.