Who taught Boruto the shadow clone Jutsu? In the anime, episode 36 Kakashi asks if Boruto's father (Naruto) taught him the jutsu, but he replied no. If Naruto didn't teach Boruto, then who did?
Now this is just my opinion, but I believe that the kids of Boruto's generation are much more talented as compared to people of Naruto's. When Naruto was in the academy, all he had to do was perform Shadow Clone technique to graduate. However, with the current generation, everyone already knows the basics. So we can safely assume that nearly everyone knows how to perform the basic shadow clone technique. But Boruto might have seen Naruto perform the Multi-Shadow clone technique (since he uses a lot of them to perform his duties as a Hokage effectively) and would've tried to replicate it on his own.