Player can earn DIAMONDS! achivement without actually mining diamonds

I was in a world, trying to earn the achievement "Diamonds to you!", by throwing my diamonds I had found in a village chest at a zombie. Upon picking up the diamonds again (the zombie didn't pick them up anyway) I somehow earnt the achievement "DIAMONDS!", even though I actually hadn't even made a single pickaxe!

For reference, the achievement "DIAMONDS!" requires the player to "Acquire diamonds with your iron tools.", of which I had none of. Could I also potentially suggest changing the description to "...your iron pickaxe"?

In addition, I later had a friend come into my world to help me earn "Diamonds to you!". When they picked the diamonds up, they earnt the "DIAMONDS!" achievement as well.

I set the security level to Private because, this seems to me to be an exploit.

To reproduce this issue: It's pretty self-explanatory really, but

1. On a Xbox account that has not yet earnt the achievement "DIAMONDS!", create a new world. 
2. Find some diamonds in a chest, or have another player mine them and give them to you.
   1. Optional: To make it easy, I've attached my world save below. I should already have some diamonds in my hotbar.

Expected result: Diamonds get picked up, nothing happens else.

Observed result: Diamonds get picked up, and player earns the achievement DIAMONDS!.