Forms response score greater than defined in the survey

Hi, 

I created a survey with some score questions and had defined the score as 0 -10 (Very Poor to Outstanding) for all score questions . Out of the 15 responses received, one response had a score of 11 and 12 for few questions although I had set the question only for 0 - 10 values. 

How is it possible to get a score of 11 or 12 for a question designed to receive scores only upto 10? Any feedback would be much appreciated.