The Gemara distinguishes between selling to a regular person and the donation one gives to the Temple of a sacrifice as follows. When one sells to a regular person, it is no longer referred to as the original owner’s animal, rather the new owner’s animal. However, in regards to a sacrifice, it is still referred to as the sacrifice of the original owner, despite the fact that it now belongs to the temple. Therefore, when one promises to bring an animal as a sacrifice, it is not considered that he has ‘sold’ it, and he will not have the obligation to pay four or five times.
The question is, who cares about the semantics? If the Torah requires one to pay four or five times if he has sold it, and that means that he has transferred it into another domain, what is the difference if it is still referred to as the original owner’s animal? למעשה, it is now in the possession of the Temple!
It seems clear that we are not just dealing here with an issue of semantics, but rather, the very fact that it is referred to as the animal of this person shows that there is still a relationship between the person and the animal, despite his having donated it to the Temple.
The truth is that there is an ownership that he retains completely, despite his having donated this animal. That is, that he still retains the exclusive right to use this animal for the purposes of his own sacrifice. If, let’s say, he has an obligation to bring a korban Olah, this animal is still his in regards to fulfilling his commitment, and no one else may use it. It is referred to as “Reuven’s olah” (as per Rashi).
Thus, the character of one’s transfer in regards to hekdesh is completely different from the character of one’s transfer when one sells an item. Making an animal hekdesh just means that the owner will use it for a specific use which involves the Temple and the holiness that applies to the animal because of that. The animal is still connected to that person. Selling an animal to someone means that it completely leaves the ownership of the person who is selling it. Only then would the one who stole it have to pay the four or five times.
(Important to note, as Rashi mentioned, that despite the fact that it still belongs in a certain sense to the one who has donated it to the Temple, in another sense it has been transferred out of the domain of the original owner insofar as the slaughtering that the thief does is not considered as if it was done to the original owner’s animal. It requires further thought to determine if the animal that the thief has donated is now called his sacrifice. The indication from the gemara is that indeed it would be called that.)