Revealing mistake: When April O'Neil first tries to take pictures of the foot clan activity at the docks, almost every time they show her phone, the screen is black. In fact, when she finally tries to get the shot of the Vigilante we see a clear as day reflection of herself on the screen.
Revealing mistake: At the end of the movie, the Turtles accidentally destroy Vernon's new car. If you look closely at one of the last shots of the movie where you can see the car now upside down, you can see the car doesn't have an engine, presumably to make it easier to flip.
Revealing mistake: When April first takes the photograph of the symbol, she actually has the camera in selfie mode, you can see her face on the phone.
Answer: Sacks told April that he was raised in Japan by a local sensei, and that he shared the lessons he learnt with her father. Splinter would have overheard Sacks mention his master at the lab, as well as when O'Neil discovered what he was up to with Project Renaissance and his connection to Shredder and the Foot Clan.
Sierra1 ★