Anything where they change the code is "an update"
Some folks really try to nitpick terminology, but usually contrary to most software lingo out there.
Anything is an update. However HTC decides to number it "is this 2.18 p9? Or do we go to 2.19?" is up to them, but it's still a patch either way. It patches your existing installation to include new code and content.
A new VERSION would be so totally different as to require a full reinstallation (such as AH 2.0 compared to the previous AH 1.x version it replaced). Similar to comments about future "AH3" and whatnot.
But then grammatically speaking, the version (lowercase spelling to differentiate previous use of word) of AH can still be updated with a patch... <-- you can see how the words have multiple meanings and folks pick and choose what meanings they want to emphasize to try and nitpick the topic to death.
It's not the first time.
[EDIT: This is all in relation to how HTC does it. You might see variation in terminology in other games]
