To avoid some dumb semantic thing because you keep phrasing it that way, no one is claiming that Ian Happ has had bad luck every single day for 5 months. The BABIP swings, to use a maybe simpler example, show that (.311, .348, .200, .196, .303 per month).
They're claiming that on the whole his results have not been as good as you would expect based on a vast sample size of hitters who have hit the ball (and struck out, and walked, etc etc) like he has this year. The results are the results, no one is saying they should like, award him extra batting average points or something. But there's really nothing in the overall data set that says he's lost a step as a hitter, and we should expect diminished production going forward.