There’s a small mention of beef bones having been customarily thrown away and I have doubts that that could be true at all levels of society - unless there was some Vietnamese cultural thing against it that no longer exists.
He did speak a little distainfully of taking pictures of your pho or having your phone handy while eating.
I think the lack of pictures emphasizes focusing in the moment and enjoying the experience and then remembering it fondly later.
.. or skipping reading the article if you look at it during some short break
The purest phở is the one that exists only in your imagination.