I do not think so. I have strong faith they do only have your chat, and no chat of others. Riot has take draconian interpretation that context of chat has no value, as they have got too much complaints that the worst flamers get free due report scoring system. For them, what other players do, is nothing. If 1 to 4 other players flame worse than reported player, it does not matter, as they did not report each other.
Riot has taken simple stance: it is easier to side with bullies than do things properly. Context is a female breeding dog, and Riot does not want to ban lots of players by screening chat of reporting players too. Riot does not want justice, but tool for vengeance.