As Flaneur said, if you never usually have a problem with ejaculation, this is nothing to worry about.
Actually, I know quite a few males who would love to do this and would envy you right now. Orgasm and ejaculation are two seperate things that usually occur at the same time (obvs) but it is possible for males to orgasm without ejaculating. I am not 100% sure but I believe this is the goal in Tantric sex, for me though, I have more experience with it because my partner and I practise orgasm denial. Due to this interest, I have come across this "skill" and men who wished they could do it and men who can do it.
The reason being is that men can have mulitple orgasms, or orgasms that do not leave them "drained" or lower their arousal and so on...Also in orgasm denial, men do it to deny themselves or keep themselves in an aroused state while still having an orgasm.
I don't know how you managed this. My partner can orgasm from prostate stimulation too, but he also ejaculates every time with the orgasm. He describes them as feeling different from a standard, penis stimulation orgasm, but he still ejaculates from them and has contractions. When this happens, he usually loses his interest as he hits his refractory period. Orgasm without ejaculation is supposed to avoid hitting that refractory period, so the male can go on and on having multiples.
If you want more into about this, I recommend checking out some info on Tantric sex, as well as some stuff on orgasm control and denial. I am sure Google can help. I typed in "How to orgasm without ejaculating" and got 423,000 results. It happens and you can even train it!
However....its probably not wise to do that when trying for a little one! lol xx
Honestly, if this does not usually happen, I seriously think you just managed somehow to experience this amazing experience and can chalk it up to a memorable experience. If it happens often, without you trying to do it, then it might be worth seeing a doctor, and finding out more information about something called "Retrograde Ejaculation" which is a medical condition in cases where it isnt purposeful.
Good luck! xxx