The Help section does not currently mention anywhere that random resource gain and random resource loss were changed to be biased towards the lowest resource and highest resource respectively, so an entry could be added on the Card Terminology page to clarify that "random resources" is not neutrally random.
I mentioned this to theultramage in chat, and he found https://arcomage.net/trac/changeset/2060/ and https://arcomage.net/trac/changeset/2060/, which are the specific changes in question. They were mentioned in a changelog or two, but there's no corresponding documentation update that new players would likely ever see.