Welcome to the world of sweeping generalisations.

It seems to be based on the assumption that ordinary feed is going to be layers pellets/flock raiser/chick feed etc. The thing you need to notice is the word "commercial" is missing.
So there's your first clue. Chicken feed isn't quite so chicken feed when it comes to the money; money for web sites, blogs and of course the feed manufacturers.
Don't get me wrong. I buy commercial feed. I've fed commercial feed at one point or another to every chicken I've known. It's very convenient and probably works out cheaper and better for chickens than trying to make your own balanced feed.
Next you have to interpret that treat word. If you fed your chickens 50% caviar and 50% commercial feed they will probably do just fine even if they did start speaking Russian...well, we wouldn't want to feed them any of that sub standard caviar from anywhere else now would we.
On this site it seems treat foods are cracked corn, mealy worms and the high carb, fat, sugar and salt stuff some humans are so fond of.
Of course not everyone in the world does feed their chickens commercial feed but they seem to live. Some may say yes but they aren't getting optimal nutrition and are likely to suffer from health issues. Depends really doesn't it? It depends on what they get fed.
Stuff like salad, most fruits and veg are fine in the same relative quantities a human with some knowledge of healthy eating might eat.
Then there is the complex issue of the type of chickens you keep and how you keep them. If you keep free rangers you can wave that 10% goodbye and ime another 30% to 40% with it.
High production breeds are going to require more of some nutrients than a hen that lays say 100 eggs a year.
Let me give an alternative method of workiing out what to feed your chicken.
Find out what your weight should be for your height and build. Now go and stand on a set of scales. If you are more than 5% above the recommended weight for your build then feed your chickens the commercial feed and try and work out what 10% of their daily feed intake is.
If your about right on the scales you probably know what types of treats are bad for your chickens and engage the brain with that knowledge for another omnivor who if female has special calcium requirements.