The provisional rule 809.02 does not allow calling a provisional in this situation. If anything, GB should get two practice throw strokes for taking that second shot and holing out from it or a misplay which would be the same 2 strokes. Although taking provisionals has been regularly recited during player meetings when players are unclear on rulings, the provisional rule explicitly indicates the times when it can be done. B.1.a. "The status of the disc cannot be readily determined because it may be lost, OB or have missed the mandatory; AND b. The group agrees that a provisional throw may save time."
In this example, the status of the disc was known and the group agreed GB could take a provisional. The rule requires both clauses to be true with the AND connector. This was not the case. Thus, GB could not take the provisional per rule even though the group indicated he could. His provisional throw was actually a practice throw along with the throw he holed out from that throw. Had he realized the correct ruling before throwing the provisional, especially since he was parked, no need to throw the second shot even though originally calling the provisional.
In the phrase "To save time, a player may declare a provisional throw any time:" the word "when" should replace "any time" to reduce confusion that provisionals can be called for any rules situation.