At a guess: LO is requesting (via mmap) enough memory up front to represent a full spreadsheet with data in every cell from A1 to the bottom-right corner, and letting the OS supply pages for the small parts of the spreadsheet that are actually accessed. AIUI this is a common technique for big sparse arrays.
RES isn't physical memory, either. I can happily have, say, 30 GB RES on a system with only 1 GB RAM (and no swap).
smem's measures - USS, unqiue set size (unshared pages) and PSS, proportional set size (shared pages divided by their share count, ie. how many tasks share them), are far more accurate and easier to reason about than RSS and VSS.
Well, RES is physical memory, it's just some places where it gets reported don't account for physical memory that is being shared between multiple processes.
If I have a process that says it's using 1GB of RES, then you can guarantee there is at least 1GB of physical memory in use. It just might also be in use by other things also reporting their own RES usage.
The next one on the list is Firefox with 8.5 GB VIRT and 994 MB RES.
By the way, I've got 16 GB of RAM and no swap. Anyway all that empty memory between VIRT and RES doesn't go to swap, it's really virtual.