Did my sonographer reveal the gender by accident?

I had a 16 week private scan and we made it very clear to the sonographer at the start that we did not want to find out the gender till birth. The lady referred to the baby as ‘little one’ throughout the scan and then toward the end I heard a he slip out. I’m now feeling like my big surprise has been ruined. This was a well trained sonographer I wouldn’t have thought they would do this.