Yeah, I remember that; I occasionally used a Scope Lens Sniper Kingdra set in gen VII. I just found it unusual that I did this (with no held item), then replicated it two times afterwards, hence my "seemingly" statement. I couldn't find anything online either. It's certainly possible that I just got insanely lucky with the RNG.Dynamaxing does not increase crit chance, but crit chance was buffed a few gens back to where Focus Energy + Super Luck or Scope Lens = 100% Crit Rate, which is also why Crit damage was lowered from x2 Damage to x1.5 Damage. Without Scope Lens it's still like a 50% chance so it isn't unheard of for all three Dynamax hits to Crit.
The best user of Focus Energy + Scope Lens + Sniper has got be to be Kingdra, though. Due to how crits work they ignore stat drops on the user so it can spam Draco Meteor without damage decreasing each turn.