thanksforallthefish makes an excellent point about perspective. I watched the video again, this time looking for clues regarding relative positioning.
When you watch the CNN video, closely watch the relationship between the waves in the foreground and the Ady Gil in the distance. Using your peripheral vision, watch the action in the background.
Here is what I saw:
The ship taking the video appears to be relatively stationary throughout the video. It seems clear that the Shonan Maru definitely makes a radical turn towards the Ady Gil.
The Ady Gill appears to be almost dead in the water for most of the video. When you compare the CNN video to the video shot from the Shonan Maru, this is confirmed. If you look at the wake of the Ady Gil in the Japanese video, the Ady Gil is not really moving (there is almost no wake).
At the last second before being rammed, the Ady Gil appears to accelerate and pull forward slightly. Again, looking at the video shot from the Shonan Maru, you can see that just before the ramming the Ady Gil accelerates and develops a wake. You can even see the wake develop in the CNN video.
As the Ady Gil accelerates forward, the Shonan Maru makes a correction to port to ram the Ady Gil that is moving to it's port side.
After the Shonan Maru rams the Ady Gil, the Shonan Maru keeps turning to port.
I think it's important to view both the CNN video and the video from the Shonan Maru to fully understand what happened. Pay partucular attention to the wake of the Ady Gil during the entire encounter, especially in the video shot from the Shonan Maru.
In the Japanese video, it appears that the Ay Gil is, in fact, driving in front of the Shonan Maru. However, when you look at the wake of the Ady Gil you realize that the Ady Gil is dead in the water. The CNN video makes it clear that it is the Shonan Maru that is turning to ram the Ady Gil.