If it has logic to only allow it to be 1 drop per raid group (assuming all members are eligible), it’s much higher than 1%. This can only be confirmed if there is evidence of it dropping multiples in a single kill. The fact you’ve seen so many, if that is the case, it’s got a pretty reasonable drop rate since 3 per 22 kills is very high.
It very well could be but like I said, my gut says it is higher. Obviously only Blizzard knows for sure.