House, a 24-year-old lefty, was drafted out of high school in the 16th round in 2008, and has steadily been working his way through the system since then, spending the last year or so in Triple-A. He's a starter, but don't look for him to fill that role in Cleveland. He was likely called up to help a taxed bullpen that had to throw 7.2 innings Friday night. He has a 2.41 ERA in 7 starts so far this season, with a modest strikeout rate, but strong walk and home run rates (avoiding home runs is something he's done well throughout his minor-league career.
Lee, a 27-year-old righty, pitched 1.1 of those innings and has appeared in three of the last four games. He's also carrying a 4.76 ERA (and an identical 4.76 FIP), and with lefty Kyle Crockett having joined the team yesterday, Lee is a logical choice for demotion (because there are only going to be so many southpaws).
It will be interesting to see how long House is up here. Is this a temporary thing, just to mix things up, or will he be transitioned into a relief role more permanently? I don't see him as someone who's ever going to crack the MLB rotation for anything more than a spot start, so maybe the bullpen makes sense.