When Family Matters premiered on ABC in the fall of 1989, it was little more than a pale imitation of The Cosby Show. You had an African-American family, sitting around relating to each other in loosely plotted stories. The show didn't really develop its own identity until Steve Urkel became a regular. This would eventually lead to the show doing decidedly non-Huxtable-esque stories involving things like robots, cloning, and time travel.
Never was the Cosby influence more evident than in this episode from late in the first season. In 1985, The Cosby Show had done a story where the Huxtable children performed for Cliff's parents on their 50th anniversary, as seen in this clip.
While the Family Matters episode in question is far from a direct lift - it involves eldest child Eddie shooting a music video for a contest - it's certainly an attempt to capture the same feeling. The problem is that while the Cosby Show Ray Charles number was unbelievable in a charming way (watching it, you almost wish you had a family capable of pulling together to put on a show like that), the Family Matters rap is just bizarre. The song isn't catchy, the jokes aren't funny, and you never believe that Eddie wrote and directed it himself.
Now, yes, I'm insulting a sitcom episode from 1990 for no reason at all. But my point is this - this is a series with no real reason to exist. This scene is strange, but mostly it's just laughably bad. By allowing a supporting character to completely take over, the series became something intensely memorable. Say what you will about UrkelBot or Steevil the Dummy, but you won't soon forget them.