How exactly did it imply that?

I can't imagine any other purpose for citing a law that carries penalties for failure to respond while you invite a response.

Yes, but whether or not it’s explicitly stated doesn’t really change the law.

Ultimately I don’t really get the big deal. It takes 5 minutes to reply to this, and if you don’t unless you’re some huge organization no one is going to waste resources bringing you to court.

It’s not that they’re implying that it is illegal - it’s that it is.