But the point is you can’t see these posts from a particular account. It makes interaction between the two accounts a bit more difficult and so a bit less likely.
The blocked person can obviously create a new account and bypass that block to some degree, but as other have mentioned it will prevent them from reposting on their main account
Yes, the article says “engagements are still not allowed under blocks”. Then again, interaction in the general sense can still happen (you can always take a screenshot and post that).