Your example is extremely simple and could work for a new coder but once things get just slightly more complicated things get messy. I can already find exceptions in your very simple example: how exactly are user supposed to be alerted? Do all users have a mobile number so they can be texted? If not do you try email? What if they are online, do you send an im-message? Should you send to all available addresses? In which order do you prioritize message if you only send to the first available destination, email first or sms first?

The most important part is that the user is not spec'ing in the dark, instead they are modifying existing behavior to suit what they want.

You cannot just give a smart person with common sense some pages of API docu and suddenly they are software architects. This takes years of experience to do. What you can do is be a code monkey and solve a very specific small problem space that an architect has assigned to you.

His point is that the inherent complexity of the problem is fairly trivial, and he stated it concisely. And you are correctly pointing out that to realize the solution to the problem requires a great amount of work and expertise. Meaning, the actual programming has a great deal of additional (accidental) complexity.