Raisel Iglesias allowed 52 hits in 72 innings pitched in 2018 (that’s good). Twelve of those hits surrendered were home runs (that’s bad).
As one would expect, there’s a decent correlation between home runs allowed and ERA. The lower a pitcher’s HR/9, the lower the ERA as a general rule. Keeping the ball in the park is a skill that translates to actual value.
Iglesias’s HR/9 rate of 1.5 and his ERA of 2.38 jump out as an outlier on a scatterplot comparing the two metrics. It’s an exaggeration, but not a gross one to say that the only way Iglesias allows runs to score is if someone hits the ball out of the park.