Growing up overnight?

Saturday we took Ansh for his Typhoid vaccination. I did not tell him beforehand that he will get an injection. He's always been scared of injection , like all little kids. I also insisted that Abhi accompany us coz we may need to hold him down.
At the doctor's chamber while waiting for our turn, Abhi told Ansh about the vaccine. Abhi also explained how this vaccine will protect him from getting a big illness.Ansh did not react & kept doing his own thing.I was pretty sure Ansh did not hear Abhi properly & perhaps did not realise that he was going to get an injection.
Once inside the doc's chamber, we got the normal check-up done- weight & general physical check. And then the doc took out the injection & I was watching Ansh closely. He did not seem scared at all. When it was time to give him the vaccine on his thigh, he coolly took off his pants & sat up. We told him to close his eyes but he said he wanted to see. So, while Abhi held him loosely, my strong boy saw the needle go in & come out & smilingly said that it did not hurt at all. I can't tell you how proud I was of my little boy. The doctor was also so happy with him & commented how he had grown up.
And all this happened to a boy who cries at the drop of a hat at home.When Dadi force feeds him, he cries, when he wants to accompany me to office & I can't take him along, he cries.
When we came back home, I praised him in front of everyone at home & he beamed. He then called up to wish his Naina Ma'am a Happy Teacher's Day & narrated the entire incident to her with pride.
We've always told Ansh that it's OK to cry if he gets hurt. So, how did this happen?How did my boy grow up overnight?