Twitter doesn't ever claim its bot numbers are 5%. Only Musk says Twitter says that. Twitter says its mDAU (critically important distinction and definition, check SEC filing for what it means) is under 5% bots which is a different number entirely than what you might think of as "bot count". Musk is knowingly and intentionally confusing the two to get people to think Twitter is lying about their numbers. If 50% of the accounts on twitter were bots it would not matter to what Twitter's actually saying in their SEC filings, which is that the users logging in daily using hard clients that display ads is <5% fraudulent.
That's exactly it, a bot using headless client or something would "view" the ad (trigger download of the ad, etc.) but not be a real person (no eyeballs on the ad). Hence, that instance of the ad display was fake/fraud/bot. Customers of twitter (i.e. people paying twitter to show their ads) are interested in this number. Also, investors are interested in that number. Twitter says <5% of its ad-showings are fraudulent - this lets investors say "Twitter's revenue is mostly genuine". That is why the metric is reported - it's for financial/investing purposes, not a claim about how full of bots their system is.
In concrete numbers, twitter is saying there are 1 billion twitter accounts, but most of those are bots or inactive accounts or API accounts or people posting through Tweetdeck (no ads) or joke/duplicate accounts or developer test accounts or... but 230 million of the users per day use a client that shows ads. And of that subset, less than 5% are generating those ad views fraudulently.
If twitter's been lying about that (i.e. their revenue) all along to the SEC that would be a problem for twitter, though not a big enough problem for Musk's claims in his Notice yesterday to work out in his favour.
