Running into catcher/UC ejection

[RKBUmp]

From your description of the play I dont see any action that would warrant an ejection. The rule about avoiding contact is when a defensive player is standing waiting with ball to make the tag. In your description is sounds more like the ball arrived just prior to the runner, the throw pulled the catcher into having to attempt a tag rather than just touch the plate and the result was nothing more than normal playing action.