How do you have a no-hitter and lose???
Error(s) and/or walk(s).
"...the top of the ninth inning, however, Johnson helped author his own undoing; with one out, he fielded a bunt by Rose and threw wildly to first, allowing Rose to reach second. Rose scored two batters later on an error by second baseman Nellie Fox."
A walk, an error, stolen base, sacrifice fly, etc.
A “no-hitter” isn’t necessarily a “perfect game”.
The Houston Colt 45s (Astros) were an expansion team like the New York Mets. Which means they got players from other teams’ let go’s.They often didn’t give good backing as a team to some pretty decent pitchers they had then. Pitchers need run support, obviously, not only good fielding etc. Any one of several things, if done better, could have secured Ken Johnson’s win. If I recall correctly, I believe Johnson’s bread and butter pitch was the knuckleball.