I think what's at issue here is the mental model at work on the part of the designers vs. this user (and other users, clearly)

For the designers/Apple, locked is clearly not synonymous with "sleep" – any device that can receive push notifications or perform background tasks isn't really asleep... it's just not the focus of my attention. Would you say your smartphone is ever asleep? Mine never is. If it's not powered off, it's constantly working in the background, for my benefit (presumably). It checks email, weather alerts, waits for calls and everything else. It may not be the focus of my attention, but it's certainly not asleep.

The author clearly wants to treat it like a traditional computer not surprising given his opening statement about not viewing it as a worthy replacement to act as one's "main device". If that's the mental model one uses, then yes, I completely see the issue – and yes, the upcoming do not disturb settings will be an all around blessing.

However, the big take away isn't whether the designers at Apple were right and the do not disturb settings will be just an added feature or if the author is right and the lack of a do not disturb setting is a huge failure.

The point is, instead, that we need to be better about understanding and predicting alternative mindsets on the part of others.

From a design perspective, this is pretty obvious... but from a consumer/critic's standpoint, it's a necessary one as well. Failing to see this subtle issue makes your criticism much less impressive and much less valuable if you're in a place to be influencing future development because seeing the more abstract difference in mindsets will (often) help you see other issues (good and bad).