Maybe he's joking, because frankly this sounds a bit suicidal. Chapter 29 of One-Punch Man hit Japan, and it's full of the decompressed, superlatively kinetic superhero action for which the manga has been widely praised. It's also only 9 pages.
It could be that the promo campaign celebrating the series' massive sales has artist Yusuke Murata feeling guilty, because he took to Twitter to apologize for the brevity and say he's going to challenge himself with a 100-page chapter next.
from chapter 30
Billboard and masks from promo campaign
The series is included in Viz's Weekly Shonen Jump digital magazine.