Activity Monitor is almost just as useless as Task Manager in terms of reporting memory footprint. Not only will Apple's API constantly hide resources from native apps (like how Safari conveniently hides it's rendering processes), but MacOS's memory model is completely at odds with their measurement techniques. Either way, you're better off using top to measure your system's footprint, if anything.
Apple's APIs don't hide anything, programs on macOS just spawn subprocesses for reasons that mostly have to do with security. top(1) is not a very good way to measure footprint, footprint(1) is (and Activity Monitor uses the same APIs internally for its "Memory" column).
