Yes you are right. That is why the bot also uses the reputation marker to make sure the author is not a spammer.
There are a lot more markers you can ad to filter out more nonsese but you will need to learn how to create a custom algorithm or find other pre created algorithms.
You can learn more here: https://github.com/Steem-FOSSbot/steem-fossbot-voter/blob/master/docs/algorithm.md
Many thanks, I will check it out.
Good luck!