BLU Medic likely doesn't know who Cheavy is, and is more confused than horrified when Cheavy goes on and on about Medic disrespecting him by running away and giving him such a hard time finding him again. Halfway into his rant Cheavy realizes that's not his Medic and doesn't really feel like doing a whole introduction. Decides to keep him around and treat him like the RED Medic (aka like shit) until he finds the actual RED Medic. Makes BLU aid in his capture with the promise of being let go once they find him (spoiler alert: Cheavy doesn't. Why would he when he could have two Medics at once?)