It's very unlikely someone bought them for him to make him look bad. Instead, a lot of the time when fake followers are created they are programmed to look 'normal' by following other accounts and engaging. Otherwise a single follow target can be a real outlier and easier to triangulate.

source: worked in spam for a long time.

Also, 10k accounts is like $5-$10 for most 'in the business'. There are a lot of services that sell for this upwards of $50-$100 though. We're not talking about a lot of investment.