That sentence does not actually make sense and is clearly in error.
Data cannot be statistically significant or insignificant. Only relationships between data, the product of statistical tests, can be spoken about in these terms.
If the question is: Can we drop data from our analyses because the inclusion of that data means we cannot reject the null hypothesis? The answer is — obviously, I hope! — no. The message you've cited is a news report, not a scientific paper. Had it been a paper that was reviewed, it never would have gotten in.
Probably, data was not included because there are substantive reasons to not include those data. Probably, as others have suggested, the excluded data was incomplete or collected using different or incomparable methods.