Help me understand garage codes... I don't get it.

[thinkly]

OK. So my garage door magically opened on it's own. That freaked me out, so I erased all of the stored codes from the opener. That made it so none of my transmitters nor the homelink systems in my cars worked, just as it should have.

I then pressed the learn button and one by one activated each remote.

My question: How is it possible that I didn't have to do anything to the transmitters? It seems to me that the transmitters are still going to be transmitting on the same frequency because I did nothing to them. That makes me think the person's transmitter that previously opened my door will do the same thing.

Although it shouldn't because all of my remotes were rendered useless until i relearned them. How does this work?

[pushkins]

The remotes are the transmitters, same for the Homelink. When you pressed the "Learn" button on the garage door opener it sends out a new "rolling code" then when you press the button on the transmitter it learns the new code.
Most garage door openers use "rolling codes" this is supposed to make it very difficult for other remotes to "happen" across your doors numbers and visa versa. I have seen situations like yours either with power failures or random occurrences like you have experienced (power surge maybe).

It used to be many years ago that there were a relativity small number of codes, so those of not good intent could just drive down the road and keep hitting a remote until a door opened, they might find 1 in 500 but that's as good as a key to the front door in most cases.