I don’t know of any places where native lawns are actually against the law, but the parent might mean “against the terms of the HOA”, which is effectively the same thing since HOAs can levy fines and in some cases evict you if you don’t follow the rules. Most HOAs have strict policies stating that you must have the kind of perfect all-American lawn that is at issue here... just one more reason why they should all be destroyed.

There are definitely city ordinances which would prohibit it, but there are often workarounds and loopholes involving landscaping (like adding a retaining wall along the sidewalk, or maintaining a small strip of grass adjascent to city property).