max behavior

my beagle mixed(max) live with me, my girlfriend, my brother and my very old mother. He loves everyone in the house and likes to play with us. My mother got ill and was hospitalized for about 2 weeks. When she came back home from the hospital my dog ignore her completely and even avoided look to her. My mother got really sad about that and we did not understand up to now why my dog(max)did this to her. Could you help us understand his behavior? Thanks!!