Options on the 40 man were Corbin Martin (just came back from injury and has given up runs in all three appearances this year) and Bradley Blalock (AA starter who's been great so far). So does make sense that they would much prefer Koenig.
As incredible as Frelick's defense was last year, it's been very disappointing so far. I guess we can chalk the first couple weeks up to the spring training juggle, but feels like a lame excuse.