Bribe and Tips

About 2.5 yrs ago my mom was admitted to a hospital. One day when my mom was in the hospital, my dad's vehicle which was parked in front of the hospital fell off (because of uneven ground). The guard came and lifted the vehicle up and helped my dad put it in a side. My dad gave him Rs10 as TIPS for his helping nature. My dad and mom used to visit the hospital for the regular check ups. Recently, my sister's kid was admitted to the same hospital. Though it is a small hospital, they have some standard rules like visiting hours etc. During non visiting hours only 2 people can stay with the patient (because the patient is a 1yr kid). But because the guard knew my father, he allowed my father and mother to go the ward even during non visiting hours. I know that this is a mistake committed by my father and mother. When I shared this with one of my friends he said casually that my dad's bribe worked. On that moment I laughed it away. But now I realize that it was TIPS and not BRIBE. But the TIP has converted into BRIBE.
BRIBE is defined as "Something, such as money or a favor, offered or given to a person in a position of trust to influence that person's views or conduct."
TIP is defined as "A small sum of money given to someone for performing a service; a gratuity."
My dad paid him for performing a service (so by definition it’s a tip), but that has influenced the guard's behavior (so by definition it’s a bribe).
May be its just gratitude or just acquaintance.
I am Lost in Thoughts.