Reddit owns the servers which host the subreddits.

And reddit has allowed their users to create subs and become mods. Now they are taking this away.

Preventing users from accessing your subreddit

You may want to consider that these mods' actions are mostly what their users wanted (there have been polls and votes etc), so what they are doing now, is...

trying to control the website's overall behavior.

... is not very different from creating the sub in the first place.

So, yes, it is a high jacking attempt.

Don't confuse things. The Reddit company is the hijacker.