How many Twitter accounts were created in automated fashion, but designed to look authentic, and haven't yet been removed by anti-spam measures? That could conceivably be around 5% of active accounts if Twitter is doing its job.
If you wanted to inflate that number you could include account takeovers, which are a little harder to measure (created by a real person, but taken over by a botnet using hacked/easy-to-guess credentials).
And if you want to inflate the number further, don't just count account numbers — instead look at the % of total activity (likes, retweets, follows) that those accounts represent. You can reasonably expect that number to be higher, given how many dormant accounts Twitter has.
Elon has alleged that his followers include lots of bots. That's not necessarily surprising as "follow Elon's account" is the sort of thing a bot developer might program in to look authentic.