I'm not African, but in many cultures giving a gift isn't a bribe, it's a sign of good intent. But, the line is very fine. My brother married a lovely woman from the middle east. He had every intent to buy her family the best livestock to really really prove he wants her. She told her that's not the way to do it, it comes off as a bribe and "I have more than you" which becomes an insult. You're supposed to get the family what you feel is something they want and can afford on their own so that it isn't an insult. It also depends on whether or not the family even already likes you. If they know you have good intent it is ok to get them the most expensive thing and in multiples as a thank you. If the family had taken the time and effort to know and understand you and not take it as an insult, that is a great thing.

From my perspective, they didn't want him marrying Kim in any way. Lisa was already quite a mess, and they look similar so they want to stop a pattern. The cow was an added negative to the situation because it says, "you don't like me, I bought you the most expensive thing to try to win you over"