Yes there is a difference.
A 'patch' is a complete operating firmware for a receiver that has some extra code added over a standard firmware. Generally a new patch will have all the latest up-to-date keys hidden inside its coding but you will not be able to read them by simply opening the file. Firmware has its uses for testing purposes and not officially illegal so is not outlawed.
A 'Key' file contains only details of keys for each provider. You can use this to update just the keys only and keep the same working firmware on your box. You can also simply open the small file and read the keys completely plain & openly. This is where its a problem because its along the lines of publically displaying secret working keys and from past history a provider has the right to get the forum removed if persued. Thats why you will find many forums wont allow keys or key files to be posted. I know there are places that do show keys, they are easily found but generally they are cat 'n' mouse places fighting back, although i have to add that recently no providers seem to actively pursue this course of action anymore. But MD makes the rules here for our benefit so thats the reason why no public posting of keys or key files.
Dont worry about your minor error m8, its good that you are giving input and at least trying to solve problems. You can always post that there is a file out, or talk about it, or pm someone etc.
Hope that clears up the difference for everyone.