Are you saying he has altered the ownership of the domain to your or your company name and address at your request ?
If he has, the normal procedure for future transfers is for you to request that the domain name is transferred to a new owner. You should get an email asking for confirmation and there are certain forms that have to be filled in. You can, if you are very unscrupulous, falsify this and transfer a domain to another party and it does happen now and then. I wish I could say otherwise but domain names held to ransom is still one of the worst things I come across in the web design world and it is also the one thing above almost all others that leaves a particularly sour taste in the mouths of those it affects.
I always register domain names in the individual name or business name of the person or company I am working for. Some designers do, some don't. Most designers, even if they register domain names for a client but register it themselves, under their own web designers name, would not object at all to transferring it to its rightful owner. Most designers who register domains like this do so because it is far quicker, simpler, and generally more convenient than the way I do it. I keep details of registration dates so that a month before the domain is up for renewal I can remind clients of this and arrange for continued use and payment for it.
I'm not sure whether I can allay your fears since no matter what you do there is a certain degree of trust involved and there are ways of holding domain names to ransom. If you're happy with your designer, if he has done good work for you and you are satisfied with the end product, then you could be reacting to something that a lot of designers do with no real ill intent underlying it. As I said, it's often quicker and more convenient to register a domain name yourself for someone.
If there is something else bothering you about the whole affair then perhaps it may be a good time to evaluate your situation and consider alternatives, but I don't want to encourage that unless you really aren't happy with the work you have had done.
Think of it like this. I can go online now, order a domain name and web hosting for it and pay for it with my credit card. The problem comes when the name and address details on my card do not correspond with my client. Things like this can halt a credit card transaction in its tracks, which is one of several good reasons why some designers register domains for clients without the clients name appearing on the domain ownership paperwork.
24 hours is about what it takes for any designer to alter an account on request, so that is about standard.
I don't know you, I don't know the job you've had done or the designer who did it but unless something else is bothering you I'd say you haven't experienced anything that isn't quite common practice. I'd also like to put this to you: the fact that your request was so speedily dealt with is encouraging, don't you think ?