Polyp expansion and grouping, IMO are the result of intensity of lighting and water quality, during it's growth.
If you were to take 2 identical frags, and put them in 2 different systems, with different lighting and params, they will look a little different in 2 years.
They will be similar, but have subtle differences.
This isn't to say that a Monti won't grow like a Mont ( structure, color, etc.) but I think environment does have something to do with it.
I agree with you, it doesn't look like any Goniopora I've ever seen.
I have a lot of Red Cap, and that's what it looks like to me.