Hacker News is currently sitting at 130 MB. I simply do not understand how these things are calculated but I suspect the calculated amount that the Chrome tab diagnostic isn't a consistent way of comparing to other application memory usages, or at least a mental model that makes sense to most people (e.g. whats a lot of memory consumption? what should it be? is it too high, is it too low? etc.)
That's not the same metric here. 700mb is the size on the App Store. What you're saying is the size in RAM.
Do you mean the RAM used by the tab? The article is talking about disk space