No, your opponent wasn't hacking
Pokemon is a complicated game with a lot of weird and unexpected interactions. Bright Powder can make you miss 100% accurate moves, Hisuian Zoroark can make fighting attacks whiff on what appears to be a Kingambit, prankster Copycat can let Liepard use a regular attacking move with +1 priority, Inner Focus Dragonite can shrug off a Fake Out without flinching.
I've seen a lot of posts asking if opponents are hacking, and without fail it's actually just some mechanic or interaction the poster isn't familiar with.
When you see something happen that doesn't align with your understanding of the game, your first thought shouldn't be "someone altered the server software to create this incredibly niche interaction" but rather "there's a gap in my game knowledge".