I find it odd too, thought for sure he's finish the season at Chattanooga.
I don't think bringing him directly to the Twins right now would exactly be setting him up for success. Don't mind a handful of starts in Septembet if (when) they're out of it.
If he's one of those guys who likes to pick at the corners and get swings and misses out of the zone I think he's going to have a tough time at the MLB level regardless of when he is called up, like Berrios last year. I don't think that's a lesson he's going to learn anywhere but at the highest level; if the team is hoping he'll contribute next year, I'd like to see him take his lumps this year and adjust his approach as needed next spring.