Question

What does the author most likely mean by "memory is an abstract painting"?

Answer 1

What the author most likely means when comparing memory to an abstract painting is that memory does not always record events in an objective, clear-cut way. Memory is often dependent on interpretation. Therefore, a similar event will be remembered in a different way by each one of the participants. Moreover, the memory of an event will change over time, depending on our new experiences and changing perspective. Similarly, an abstract painting conveys an idea that varies among all those who look at it, due to their different perspectives and experiences.

Answer 2

In general our memory is not of what happened at all. It is a reconstruction with some elements that are remembered.
Try this: Your last holiday,,, picture one memorable scene.... do you see YOURSELF in that scene? Like from the outside? 99% sure you do. See? Not a memory, a reconstruction.
We create a painting from some fuzz that we have lying around, shifting angles and viewpoints in the process.