"Dive bombing" when used in a story like this is an extremely subjective term. As others have mentioned, there are no details on dive angle or speeds but also, there is no mention at all of the most important part and that's training. Hitting a target while dive bombing, at night, over black water, with flickering light from flares, in a four-engined bomber with no dive brakes would be no mean feat and to do so without ever having trained for it and with no suitable bombsight impossible. This isn't even to mention the problem of the bomb bay. Even dive bombers with an externally mounted bomb had problems with the bomb hitting their props when released, that's why many of dive bombers had bomb yokes to swing them out and away from the plane but the B-17 had the bombs inside. A release at a true dive bombing angle would likely result in them hitting the front of the bomb bay.
Another interesting clue to this is the fact that they dropped on two separate targets, another highly unlikely thing to attempt in your first ever dive bombing attempt (or any dive bombing attack for that matter). You just don't have time to pick different targets and maneuver the plane between drops, you're more concerned about getting your bombs off and pulling out without smacking the water. Of course, these two ships could have been moored together but the general idea that they dropped on two separate ships is far more indicative of a shallow "glide bombing" tactic or even a low altitude level attack.
Overall, I strongly suspect Trukk's comment is correct, this is far more likely to be a glide bombing attack at a very much lower angle of something like 10 or 20 degrees at most rather than a true dive bombing attack at a 70 degrees.
