Can Someone's Stream Be Used as "Evidence" When Sending a Report?

Had a tristana that kept rocket jumping over people to ult people into them low health teammates (every ult was them doing this but one because they fail flashed and didn't get behind the person), but was trying to act cute and "mb" in chat, but in their stream (they linked it before the game started), they were laughing about it, calling it the "Cody Done", saying how they were just trying tilt us to see who would get mad first to report, and so on.

So while they were clearly trolling and saying it on stream, they weren't saying it in game, even though it was pretty clear they were trolling.