I don't know that the number matters if a) you're serious about not meaning to offend and b) you realize you're actually offending people. I only used the number to dispel the nonsense about only white people caring or something similarly underinformed that some people were trotting out.Correct me if I'm wrong. The issue you are presenting is that 10% of a group is enough when offended to act on their claim.
You missed the point of that illustration, which was to underscore that if you don't mean to offend someone and you do then it's time to stop doing that. So if you say a thing not meaning to offend and one in ten of the people you use it on are offended it seems you should do for them what you'd do for an individual.That's wrong. The percentage should be closer to your example as follows: 100%