There's nothing wrong here, but it all feels to me like a bit of a false dichotomy. When discussing the functional approach to the simulation, the author still talks about objects, such as tanks and shells, whose state gets tracked. So it isn't as if an object approach has been completely abandoned.

Similarly, there's nothing preventing an implementation in an object-oriented language from making the states of things at the beginning of a time step immutable. In fact, this is done all the time in scientific simulation (necessarily so, because you might try a time step that is too long, and have to re-try a shorter step from the same initial state).

So the author's conclusion that The second [fix] is to avoid any kind of intra-frame pollution of object data by keeping a list of all changes..., then applying all of those changes atomically as a final step sounds like a letdown to me. The imperative codes I work with do this all the time. It's just that the comments say mundane things like "Update the pressures" or "Report out final concentrations" rather than "Apply changes atomically to avoid intra-frame pollution."