Was it an illusion?
No, definitely not.
Last time, Su Yuan's battle against the Ferocious Beast was something Chen He watched from start to finish.
Chen He was certain that the power, speed, reflexes, and explosiveness Su Yuan displayed back then were nowhere near what they are now.
LitRPG: My Unique Talent Is Fate Hints
LitRPG / Adventure
LitRPG: Every Attack Gives 1 Permanent HP
LitRPG / Sci-fi
LitRPG: My Real Body Is the Cheat
LitRPG / Sci-fi
Global Stat Points: I Maxed Out Attack Speed
LitRPG / Urban
LitRPG: I became the God of Mining
LitRPG / Xuanhuan
Myth Invasion: I Kill Gods on Earth
Urban / Comedy
After the World Became a Game I Chose Black Talent
LitRPG / Mature
God-level Assassin, I'm the Shadow
LitRPG / Urban
Global Panic: The Gnoll That Farmed the World
LitRPG / Urban