Twitter has never claimed that the number is accurate nor important in absolute terms (“we aren’t sure” features prominently in their filings!) rather it’s a number that is important for understanding growth and evolution of the platform. The number matters quarter-to-quarter, not in isolation.
Active human users matters in the context of advertising, it’s a pointless distraction that musk is employing to back out of the deal.
Let’s imagine there is a real measure of “non-human users” and lets say it turns out that Twitter underestimated by 50%… so? Musk long said he wasn’t buying Twitter as a financial move, and that he has a plan to be wildly profitable off of a small proportion of twitter’s users so unless 95% of twitter’s users aren’t real, it doesn’t impact his (absurd and ridiculous) plan.