From reading various things from Dan Szymborski, it sounds like it's WAY more innings than you think before you can start trusting it. Like 500+ innings.
In this case too like Squally pointed out Assad's not actually generating soft contact, he's just stranding a bunch of guys on base. So it's overwhelmingly likely that Assad is not one of those unicorns like Hendricks that can do this year in and year out. Which is fine, even once his ERA catches up to his peripherals he's still very valuable. No one better complain about a SP with a low 4's ERA making the league minimum that still has a couple minor league options.