We can't know if Google's email app has to do something special when it handles links to Google's (same Google as the email app's) video service.
I can tell you 100% that Aqua Mail does not *willingly* interact with YouTube, Chrome Cast, or anything video.
Maybe the normal things that it does (checking mail, posting notifications) do have the side effect of somehow messing something up, but:
- I don't own a Chrome Cast device (dongle? whatever are those things properly called), don't think our QA has them
- I can't think of anything in Aqua Mail that runs exactly at 5 minute intervals (at least with the default settings)
- Some other app (Aqua Mail, "other" relative to Chrome Cast) doing "something legal that it needs to do" should not have any effect on a whole different app. Android is a modern multitasking operating system, it's not DOS, right?