Some folks also have the ability to “Vouch” a submission, to counteract the effects of flagging, but enough flags can override the vouches.
Posting your own work is OK. My guess is, some people did not think it was real. You can always email the moderators (hn@ycombinator.com) to ask. Do not be scared or shy.
I thought it was a good post. I hope this does not scare you away.
Personal stories are more difficult, someone will claim it's fake, some will disagree too strongly. They are not forbidden, but nobody is sure how the hivemind will react.
Because each individual had their own individual reasons, there's no explanation beyond that.
For me, "my writing did not connect with the HN audience" is the only healthy way to think about flagged submissions (and downvotes too). Because better writing (or more attentive story selection) is the only thing in my control.
It's feedback and feedback is invaluable. Good luck.