From my understanding the position of the objects are different between NTSC and PAL. So if you set it to display NTSC you see the enemies in the wrong positions and the collisions are calculated on PAL.

Note: I'm not 100% sure I understood the article correctly

I found the article quite confusing I have 3 possible understandings:

1. The one stated above

2. Collision is extremely fast and not displayed on screen ( if was displayed in screen it will be easy to spot by going frame by frame )

3. Something else collided with something else. In the article it talks about the fish with the health bar