Sorry I didn't get back to you sooner, I ended up being way busier this week that I expected.
So it looks like a significant strike in our game is a strike that causes damage above a particular threshold.
Since it's tied to damage it's not as simple as saying "this strike is a significant strike, and this one isn't", it will be influence by many factors.
But for the most part it would look like jabs are not significant strikes, and most other strikes will tend to be (still based on the damaged landed though).