You read post number 2 above?
On the fly multisport: Start first activity as normal, running in the OP's case. Once finished press stop as normal to show the usual resume, save screen. Now press and hold the down button to bring up the sports activity screen, change to whatever is the next activity, bike in the OP's case and carry on as normal. At the end save as normal and all activities are saved under one multisport activity.
After pressing stop, then? If I press the down button, I get to the normal watch face.