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1. Sponsors can and sometimes do bot their sponsored streams without the consent or knowledge of the streamer in order to increase visibility. For obvious reasons, this only really happens with sponsors that pay a flat rate. They (the sponsor) basically see it as part of their advertising budget.
2. Other types of sponsors pay based on viewer count. When streamers get a sponsor like this, they generally request to be on the front page for the sponsor period. This gives them a free viewer buff, meaning more money, and the sponsor is happy too, because more people see their ad. Some sponsors will even request their streamer do this.
3. Schizos on 4chan with no connection to the streamer can buy bots for a stream to cause drama. See Hololive EN.
4. Sponsored streams in a game that has drops will draw a bunch of random new users who basically behave as bots because they are just leaving the tab open to get free stuff and not actively watching or participating in chat.
5. In rare instances some streamers do bot their sponsored streams that pay by the view. This is considered scummy and very few streamers will do it, because if they are caught they will probably not get many more sponsors.
6. Attempting to track bots by tracking users is a fool's errand. Real Twitch bots often include actual accounts that sit in the chat. Some of them actually post messages.
In short, there are many explanations for why there is a sudden spike in the viewer graph, and none of them matter. Get a new hobby, you fucking number subhuman. Kill yourself.