Its an injury. Yes constant close hand feeding, and only that, can cause a muscle weakness over time from lack of extension. This is not the case. The cham didnt slowely lose range, it didnt slowly lose aim. It hurt its self. Id say 75% of mine over the past 25 years never made it to death with a perfectly functional tongue.
Its just the nature of the beast. You didnt do anything wrong, its not a husbandry problem, there is nothing you could have done to prevent it.
It might gain use of it again in a few days/weeks/months. But during the mean time (and maybe forever) you are going to have to hand feed it like a bearded dragon. You are going to have to get the food and hold it 1" from its mouth and let it eat. You might want to invest in some long tongs, as sometimes they have trouble with the hand and small prey.
"Harry" lost the use of his tongue at 1 year old, he is 5, ive been hand feeding him or using tongs right in front of his face for 4 years and he could care less. The only way i he can hunt now is if i place silk worms randomly around his cage and let him run around and lick them up like pop corn, since silk worms never run.