Oscar was the weight a few weeks before the fight because he planed on moving down even more in his next fight. Instead of coming in at the right weight that would give him the best chance against Pac, he was already thinking about going down to 140 which he admitted was a huge mistake.. I think there is no question about Oscar being weight drained. Being weight drained doesn't necessarily have to mean you are dehydrated, but that in losing too much weight, you lose muscle, stamina, strength and speed.
When a fighter drops down a weight class, and is slower than they were at the higher weight class, then you know. Which is exactly what I saw in Oscar. You can be completely hydrated to the point where you are pissing pure water, and still be weight drained... Going through intense workouts without the proper calorie intake will make you lose weight, but it will eventually have an ill effect on your muscles. Probably even more so when you are in your mid 30's, and past your physical prime.