On this subject, I actually just wrote about this and why I believe his start is legit. Basically, his BABIP is about normalized relative to his contact profile and his xwOBA/wOBA ratio suggests that, if anything, he has been unlucky, so as long as he maintains his contact profile and his K rate doesn't jump astronomically, this is sustainable.
https://soxon35th.com/2019/05/10/yoan-moncadas-luck-has-normalized-and-his-numbers-are-still-terrific/