So it's time to debate the definitions of "significant" and "massive"?
My guess is they didn't want 'significant' to be confused with 'statistically significant'.
Suppose the new version is 5% better.
People may ask: well, is the 5% just noise, or is it statiscally significant ?
Reply: it's not just noise; the 5% is statiscally significant.
They want to differentiate between:
- a "small, but nonetheless statiscally significant" improvement ;
- a huge improvement ( in everyday language ) ;
They want "massive" to convey the latter sense.
Just my guess, though.