Alright, PTO season!
At the risk of sounding like a broken record, most PTOs don't lead to contracts. In some cases, it helps a team fulfill the CBA requirement of dressing at least 8 "veteran" players in preseason. Sometimes it seems like some people expect the core players to suit up in every preseason game. Most teams will have PTO guys to give some regulars the night off.
Looking at the Avs preseason schedule, there's a back to back on October 4th at Minnesota and one at home the next night against Vegas. I'd imagine they'd save most of the "A" squad for the home game while the "B" team gets sent to Minnesota. I'd bet a donut that Johnson is part of the "B" team and saves Girard/Toews/Byram from making a round trip flight.