do you think maybe a hog knows which dog is more scared and uses him as an escape hole?
Yup! I walked up to a bay and a puppy backed up and looked me. The boar charged him within seconds. The color does play in too. What would you do to out of something? you push until something gives and then run as fast as you can! So if it is weaker it will get pushed more. If it stands out it will get pushed more. Just my 2 cents.
IMO hogs are oppurtunistic, the large boars are noticed more because they are the ones who cause the severe damage. If the bay dog looks away and the hog feels like he can get to him he will because that will be one less dog to deal with or he will give the dog one good hit on his way out. If the dog is in a tight place and the hog sees the oppurtunity he will make a run at him.
IMO, there are boar hogs out there that hate dogs so much that they will set themselves up to kill/injure dogs rather than run away. I have seen this happen several times. These are hogs that have been dogged before.