The whole thing is BS. Twitter could have easily got an accurate number if they wanted to. And Elon could have forced them to do that as part of the deal or done a decent job on his own before the offer.
Both sides are bullshitting to negotiate a better price.
"We have performed an internal review of a sample of accounts and estimate that the average of false or spam accounts during the third quarter of 2020 represented fewer than 5% of our mDAU during the quarter. The false or spam accounts for a period represents the average of false or spam accounts in the samples during each monthly analysis period during the quarter"
I think that Twitter actively does not want spambots on their site and therefore would invest into metrics so they know how they're performing on that.
"both sides are bullshitting to get a better price"
Which implies that this number is related to Twitter trying to get a better price. However, if this is the number they have always said, regardless of the methodology, clearly they can't be trying to get a better price - as they started doing this long before there was a price to make better.
That is separate and independent from whether the number is accurate to begin with - if it's remained consistent and publicly available, there's no chicanery here, the risk around that stat has always been baked into the market price of the company.
The percentage of fake users has a high correlation with the value of the business. Twitter's value is higher if the number is lower. I'm not suggesting they just started bullshitting in the past month, just that they are not making the best effort to get an accurate number.
Having zero bots would be good, but obviously that isn't True. So instead they say a low consistent number and hope no one proves them wrong. Most importantly it doesn't appear to be getting worse.
Both sides are bullshitting to negotiate a better price.