I recently became interested in why there were 30+ almost instant upvotes on my post recently.
I started digging and came across a user named @dart - Now I am not sure he is the source of my upvotes, but it is a similar thing. Just take a quick look at a screenshot I took of his transaction history:
I won't go further into detail - if you are interested, take a look into it. He's apparently somehow creating hundreds (thousands?) of accounts at a time, and has some sort of script that makes them vote en masse for seemingly random posts. They also will sometimes post nonsense posts and upvote those as well. You can find more detailed posts about him here on steem if you look.
Just thought I'd point this out. Not sure what to make of it, but no one seems to want, nor be able, to do anything about it.