开挂

Short for 开外挂 (kāi wàiguà) — 外挂 ('external attachment') was the early 2000s term for third-party cheat programs hooked into online games. Now 开挂 is everyday slang for 'performing impossibly well', applicable to anyone's career, sports, exam scores, even kids' growth.

Casual, can be either accusatory (in-game: 'you're hacking!') or admiring (figurative: 'you're crushing it!'). Tone is read from context. 像开了挂一样 is the very common simile form ('like they turned on a cheat').