“The combo notion was introduced to competitive fighting games with Street Fighter II by Capcom, when skilled players learned that they could combine several attacks that left no time for the computer player to recover if they timed them correctly. Combos were a design accident; lead producer Noritaka Funamizu noticed that extra strikes were possible during a bug check on the car-smashing bonus stage. He thought that the timing required was too difficult to make it a useful game feature, but left it in as a hidden one. Combos have since become a design priority in almost all fighting games, and range from the simplistic to the highly intricate. The first game to count the hits of each combo, and reward the player for performing them, was Super Street Fighter II.”  
oh, you are right, it was a oversight

@RIG  
Not so much a glitch, but an oversight in Street Fighter 2 (I think. Don’t quote me on that.)

fun fact: the only reason why combos exist is because a glitch.