Yes, that's just something buggy. The helper is pinned to a sandboxed tab that is making your CPU go crazy. The data isn't being uploaded to Arc. I'm guessing you know what the tab is.
No, there was no tab in the background. I set the Arc to not restore any windows from previous session. After I opened the Arc, I only opened a google doc page and closed it before the recording. The same RAM increase and data upload can be observed without open and close a google doc page.