That is what the memo is trying to say. That no regulations or laws are changing, but it's simply pushing for a certain interpretation of the law that doesn't seem to have been the status quo for awhile.

Some stats I found online report that ~60% of greencards are granted to people already living the US. This memo makes it seem like that route will now be much harder. So while its true that the law as written has always been true, they're definitely pushing for a change that will result in past behaviors no longer being true.