Everything involving David Price makes perfect sense and I for one, applaud the way Gibbons has handled him.
Look he's your overall best starting pitcher. There's no doubt his body of work from acquisition to October was the best overall pitching performance. So you can't, NOT use him in the playoffs. On the other hand, he's in the middle of a terrible pitching slump. So you can't rely on him to be your game 5 do or die starter.
0% of managers in this league would have worked Dickey to the 6th or 7th, unless he started getting hit hard, then a middle reliver-Sanchez-Osuna, but they would also have started Price in game 5. By putting in Price, they are resting their overworked bullpen and their 41 year old starter and against a team who have by far and away their best hitters as Left handed (only Beltre stands out for righties and he's hurt) so he's a good option to preserve the lead in a do or die game.
You're trying to build Price's confidence by not having him pitch in a pressure situation since you have a 6 run lead. You are not relying on a slumping starter. You are preserving your bullpen and letting your hottest pitcher pitch your most critical game, all with one move. It's the best I've ever seen of Gibbons.