I am super sorry this was triggering. But in the self injury forum that is honestly a very normal and "untriggering" post. It is indeed triggering but many of us have been doing/dealing with this for most of our lives.
In abuse forums, people will discuss abuse. If details are put in, or its graphic it will be considered a trigger. But if abuse is just mentioned it usually is not. I am really sorry that you were upset. I just hope this might help u understand why it was not origianlly marked.