Because the picking was done 100 times, the number of times a counter appeared is the equivalent of its percentage
So blue was picked 58% of the time, and red picked 42% of the time
Then
58% of 10 is 5.8
42% of 10 is 4.2
Since you can't have portions of a counter, you have to round the two numbers to the nearest integer, so there were 6 blue counters and 5 red counters. The reason they deviate slightly from this value is just because of random outcome