Surely every culture will have anti-anger norms and literature. The parent comment is claiming that in western culture we take it to an unhealthy extreme.
I am an easterner who spent a few years in USA. In the beginning, I sort of liked how people seemed in control of their emotions in situations which would make me visibly angry. No one displayed their anger/frustration to the extent I am used to. This may be anecdotal but with time I observed that deep inside they lingered these emotions more than I would do, which as you implied, is unhealthy.
