I thought this exact thing yesterday, saw Byf's video today and he said the same thing! It absolutely does not make any sense. We killed Oryx in the middle of Saturn's rings and sent him falling towards Saturn. A quick search shows that Titan is ridiculously far away from the Dreadnought, so much so that even if Oryx somehow swung around Saturn and launched away, he would still be floating in space, even after many years. It's just not realistic in any way. One only needs to know that Titan is outside Saturn's rings and remember which direction Oryx was falling in order to see how things don't add up. So it's almost certain that Bungie knew that it doesn't make sense and decided to still go with it because the concept of Oryx's resurrection was too interesting.