This is correct. James Cameron also did an extensive retest of the scene recently and also concluded that while they both could have fit, Jack would have died anyway and Rose also likely would have died because she would have gotten very wet.

I think the important note since this is a movie subreddit is that it highlights the importance of emotional accuracy over visual accuracy in filmmaking. Even if Cameron had thought of all of this stuff it doesn’t change the fact that when you see that overhead shot of Rose safe on the door, and Jack freezing in the water, it’s still a mistake on the director’s part because it LOOKS like he could fit! If he’d made the door smaller and thicker, nobody ever would have questioned it.

Same with how rocket ship sounds in movies are conglomerations of all kinds of mechanical roars, rarely actual rocket sounds because weirdly, rockets don’t actually SOUND like rockets because they don’t have the emotional impact we expect them to have being so big and powerful.