On the long play to Shakir, he got open because a LB was spying on Josh instead of covering the WR. Josh burned them on that.
On the TD run, the D had everyone in coverage, leaving a ton of running space for Josh. Even though five defenders went after him, it was too late - he's just too fast, powerful, and shifty. Any QB not named Allen or Mahomes probably gets tackled around the five-yard line.
Essentially, his legs open up the passing game, and his arm creates running lanes.