It was orphaned because the pool that decided which block would win was the same as the one that benefitted from winning.

EDIT: I also suspect that if another pool (such as Eligius) had orphaned the F2Pool blocks that came after that in favor of your block that a subsequent F2Pool block would not have agreed and we would have had a deeper fork. I think the problem here is that everyone is relying on bitcoin-core to do the right thing when it is entirely possible that a modified version is not playing by the same rules.