It is a concept that helps understand the effects of where force is applied. Think of you fridge at home. If you wanted to push it over, you would apply force at the top. Push all you want on the bottom, you will not topple it.
Bikes are low compared to vans. Force hitting the bottom of the van would shift it sideways, not flip it. From the photos, you can see that the bike hit low. Its just strange, thats all.