I agree with you, but 7GB for 100 tabs sounds likes something unusual happened.
I usually have around 200-350 tabs open (Yes, I'm hoarding, I'm aware of it). I usually terminate their processes and respawn them when I need them (their state is not lost) but IIRC, when I don't I get around 3GB for 200 Tabs
I've seen this many times, and it seems to depend on the complexity of the page being rendered. I did close and re-open things, much to the same result.