But what's their point? Are those odd TSLA shareholders?

Most who claim that HN has a rabid and irrational pro-Tesla cult must have missed the last seven years of incredibly critical commentary. I started noticing in 2015. Maybe I'll put together a montage one day. The claims of a pro-Tesla cult are certainly more widespread than uncritical fanboyism.

Can they build in a mechanism to mitigate baseless flagging?

"most of the time dang unflags them" is that mechanism.

If I found a reliable way to automate the recognition of bad-faith user interactions I would sell it to google and retire before bringing it to HN.

edit: Also, apparently, users can "vouch" for posts which presumably is just the inverse of flagging a post.

You can vouch for a comment, but not a post. (Except by emailing dang.)

Well, for example, deducting karma (or whatever) from people who flag stuff that dang unflags.