I think it means that the number that get_user_id(numbot) is greater than the one that has been set. So it is outbound of what is possible.
new bool:isBot[33] = false
i have seem some userid up in the 3000+. So the index range that it set it 33. So any bigger than 33 i think it will give what you said. index out of bound.
Because i don't know the output of numbot. I can't help you any further than this.