I had a similar situation that was really strange... we asked a group in the UK to apply our method in their data set as a further validation. I sent them all the code and stuff, and they sent back a plot and p-value from my code. Problem is that the manuscript describing the data set was published, but the data set wasn't publicly available at the time unlike most other data sets from NIH-funded projects due to it being from the UK. So because of this, I had to add like 3-4 other authors who I had never met before for reasons that, at least to me, seemed pretty arbitrary. They eventually released the data set to the public, but it seems really strange and unfair that these people got authorship simply by refraining from publishing a data set. I mean, I'm wasn't even mad, but my then-PI dropped some wisdom on me: there is really no value in being stingy with authorship. Of course, there are criteria that need to be met to get authorship, but for borderline cases, it's better to add than to not. What is there to lose?