Tiger barbs have a reputation for being fin-nippers, but from what I've read, if their school is large enough, they'll chase each other and leave other species alone. That's probably why it's working for you.
As your personal experience grows and you become bolder but more able to recognize trouble before it reaches dangerous levels, you may find many things in the hobby which don't fit what you see.
Just as in anything else, when you first start it may be important to hear some of these rules but after a time they really don't apply to you if your tank is running the way you want.
You may find that many rules were not meant to extend past your front door.
It would take a book to list the rules I break. How about large open water African cichlids like Protomelas (insignus) with mbuna and live plants? People have commented that I can't keep them together as it will stress the larger fish too much and I can't keep the plants because the mbuna dig too much and I don't have CO2 on that tank.
But then he bought the insignus fry and the plants are still alive!