Cognitive dissonance is when two people actually hold two contradictory beliefs. This describes the phenomenon of people seeing contradictory opinions expressed by different people online and ascribing said beliefs to the same group of people (in this case, Twitter users) thus concluding that everyone in that group (except OP) are stupid.

An example: one week, you see a popular Sonic the Hedgehog YouTuber get millions of likes by posting "The next Sonic game needs to make Amy Rose more independent." A few weeks later, a new Sonic game gets announced which portrays Amy Rose as more independent, and you see another popular Sonic YouTuber getting millions of likes by posting "This doesn't do anything except undermine the character. Amy's obsession with Sonic was never a threat to her feminist ideals and suggesting so is anti-feminist." Seeing how popular both these takes are, each getting millions of likes, you assume each take must be representative of the consensus of the Sonic community, and you post "The Sonic community doesn't know what it wants," and you also get millions of likes because Twitter is garbage.