Very good question. First, don't worry. Second, please don't confuse UserAuthority with "false flagging bot accounts". Let me explain:

- my blogpost is not a published double blind-read academic whitepaper, for it contains typos, and still misses bits and pieces here and there. It was initially published in a hurry, later on I added some updates, and I might continue to do so.
- the picture containing the example follower graph contains the words "spam / bot account", where you might confuse it with a valid account of your father with the same characteristics. The picture is merely an overly simplified example to explain how UserAuthority works.
- I think your father's use case is an exception, but it might not be: I can investigate that. A user that invested some outside capital, doesn't post, doesn't network, and **sometimes** manually upvotes 1 other account (you), yet doesn't hold enough capital to be followed by many (like @freedom). 
- because your father doesn't post, he can't self-upvote nor spam.
- if your father only upvotes you, why not delegate his SP to you, or follow your voting trail? Currently he's wasting voting power, and therefore losing value due to share (vest) emissions, and that's the exact opposite behavior a bot would have.
- UA is not intended to hinder small accounts, not false-flag them, but to combat system abuse and self-curate the system. Your father doesn't seem to abuse the system, he's just not really active.
- UA can also be used as a detection mechanism to identify strange behavior, by extending it with other metrics. Extremely high frequency posting, lots of voting, high-correlation voting with other accounts (multiple self-owned bots0, and all that combined with low UA. Your father's account would not be "falsely flagged" or seen as a bot.

Cheers.