The net flew through the air; unobstructed and on target.
Joseph hadn't been able to notice it in time, and was thus unable to dodge it.

As the net began to close after hitting his back, the weights on its corners came into Joseph's field of view. Should they come sufficiently close to another, their rotational inertia would tangle up the net, preventing an easy escape from it.
However the net had no properties that interact with septima, so Joseph could simply use his frequently used gravity slingshot to push them apart before it was too late, which he successfully did.
This resulting in the net simply falling off his back shortly before he landed on the target roof, on which Joseph immedeatly took cover.

Since it would take a bit for the ground forces to get to the roof, only the VTOL in which the forces arrived presented an immedeate threat. To prepare a bit for its arrival, Joseph opened one of his suitcases to find and take out a set of boules he originally brought for entertainment.
He didn't expect them to do much against the hull of the VTOL, however they should be able to wreak havoc inside its engines, if he could get them there. Besides, some long-range projectiles are better than none.