It is clear from the article that what eats up so much RAM is not the weather app itself but the framework it runs on. There is a "Renderer", a "GPU Process",... eating most of it.
The thing that the task manager doesn't tell you is whether or not these are shared components. It may be that the 662 MB used by the "Renderer" is shared between many Windows components, so killing that Weather app may not reclaim as much space as you may hope, instead, it would require killing every user of the component, some may be core system apps.
In addition to the distinction between private and shared memory, there is also the distinction between actual RAM usage and and virtual memory. It is possible for a process to memory map a 100 GB file. If you look at the address space, it will take 100 GB more of virtual memory, even though it may be actually zero physical RAM, but it is not always zero either, the parts of the file that are currently accessed take up some space, which may later be reclaimed by the OS by committing the page to disk.
Even the most obvious "I do a big malloc()" kind of memory use is not that obvious, the OS can overcommit, put stuff into swap, use memory compression, etc... And it can do that even if the system is not overloaded, as to make more space for the disk cache for instance.
So seeing "1 GB" in the task manager is just a vague hint of how it may affect performance. And not all "task manager" tools give the same value for the same program (so Windows vs Mac may be misleading). "Process Explorer", a more advanced version of the Windows task manager can give a lot more details, with different values of memory usage depending on what you are looking at.