I think the bigger mistake is to think even if it was a good sample it could gauge people’s mood - incentives for posting to social media are either happy or outrage. You will never get a silent majority “just okay” or “neutral-low” by averaging between ecstatic and outraged.
I think the fact that two of the top ~10 happiest days in 2018 were attributed to a Korean pop star's birthday is excellent evidence that people of twitter are not, in fact, good samples of the people of the US.