Rule #1 of the moderator's handbook, is do not touch Satoshi's posts. I doubt anything was removed intentionally, although I don't know what post you are talking about in particular.
BTCTalk has probably the best staff on the internet. They never censor anything and generally leave everything alone to allow growth. Satoshi is the main creator and helped everyone and everything evolve. There is no reason for them to censor anything from Satoshi. Satoshi has documented in the original Bitcoin whitepaper along with his posts some critical info that needs to be preserved and protected. Thanks to the staff for their time effort and attitude.
If it was an accident or the moderator was just trying to be helpful and made a mistake, can it be undone?
Yep, anything can be undone. However if something like that was to accidentally happen, a moderator would normally bring it to attention, say, hey I accidentally did this, can someone restore the post? And it would be done with. I still dont know what it was that was removed though.
He says it was from
this thread. He pointed to a topic on
bitsharestalk that was posted by username "bytemaster" on that forum. There is a user with a "u" # of
611 on bitcointalk with the same username which was created on July 27,2014. There was a post by satoshi that quoted the same username on July 29, 2010. The post quoted in the OP was likely a response to satoshi (IMO).
If you are able to search by deleted posts by usernames I would suggest searching deleted posts of bytemaster