It does not say h264, but I also didn’t transcode it through fcpx.
I was annoyed with all of the data it transfered over (the multiples copies of files things you mentioned above) so I just trashed the entire event and made a new one and imported all of the newly transcoded footage (I used compressor)
Did you ever find out how to reattach a clip that you detached audio from? Compounding a clip doesn’t appear to just undo the detach. That one’s been bothering me…