He doesn't have to be "above average". He just has to be the best option on another team.
The average OPS for an OF in MLB is .733. While better than the average OPS for a catcher (.686), the bar to start for a team might not be as high as you think.
And Swihart has a very good arm capable of playing in RF. He'll have an easier time learning that position than the rigorous demands of catching.
Swihart might represent an upgrade in RF for teams like the Orioles (where OF defense goes to die), the White Sox, the Twins, the Marlins, and the Rays.
The Orioles, White Sox, and Marlins can take a low risk chance on him right now. What's he going to do? Ruin their season? (The White Sox should have cleared the path last off-season when Avisail Garcia had his career year.) Even the Twins and Rays should consider it. Outside of the Rockies and Rangers and maybe the Nationals, what team should be taking a chance on him at catcher? He's not even getting one in Boston, where the offensive side of the game has been the worst in MLB. And if the Red Sox are not giving him a chance, doesn't that say anything about his play behind the plate?