"Editing" is a fairly broad term. The entry from the OED,

d.2.d To prepare a film for the cinema or recordings for broadcasting, etc. (by eliminating unwanted material, etc.); = cut v. 21 e. Also with in and out.

So, any cutting is editing. Editing in print can deal only with page formatting, and leave content completely alone, though it generally means that someone has at least read it through for glaring errors, and can go as far as major rewrites.

"Heavily edited" seems to imply a bit more, like stitching clips together, but cutting the whole conclusion of a story out to leave its meaning up to interpretation could be considered "heavy" though "heavy-handed" might be more to the point. You don't really need to string things together to change the gist. Just showing a short window without the frame can do the job admirably. There is plenty of history of that. If, for instance, someone were to take a clip of Mr. Breitbart where he says "People are falsely saying that I'm racist!" and cut it down to a simple, "I'm racist!" it sort of changes the meaning a bit. It's just nipping a bit off the front, but...

So, yeah, I just think that saying it wasn't edited looks silly. It was. Go to the meat of it instead.

Is it EDITING to cut a tape off for length without altering anything on either side of the cut?

Yes. By definition.

Whether or not such editing is nefarious or not is another question entirely.

Trying to redefine a word with well known professional usage isn't going to be terribly successful. It winds up looking like someone with their fingers in their ears going la-la-la-I-can't-hear-you. Not the best way to bolster credibility. There are other, more solid ways to do that

You seem a bit foggy yourself. I'll give you that the "heavily" is overstating it, but cutting tops and tails is most definitely editing, especially when it's taking a short piece.

From the OED,

d.2.d To prepare a film for the cinema or recordings for broadcasting, etc. (by eliminating unwanted material, etc.); = cut v. 21 e. Also with in and out.

An excerpt is, by definition, an edited form. That is simply a fact. To claim otherwise is simply wrong.

No, this is one of two things.

Two words. Dan Rather.
He got, shall we say, overzealous with a story, didn't vet it, and was hounded from his career, which had a lot more credible years behind it than Andrew's has. If Mr. Breitbart want to run with the big dogs, he has to deal with the same sort of accountability. Nobody forced him to run with the story. If he was punked, that also speaks to his credibility.

As to the topic of this story, while "heavily" may be a bit hyperbolic, to claim that cutting a piece of video down, trimming top and tail to show the desired clip, isn't editing is simply untrue and dishonest. It is the very definition of the word.