The descriptions on the chests advise that you will receive a 5-star Quality 2 gem…
However, apparently the selection screen (where you select the six gems) is actually indicating you’ll get a quality 5 gem…
There’s a guide for how to do so…
So, what you received (a quality 2 5-star gem) matches what the chest description says you’ll get, i.e. you got the correct quality gem.
The actual bug is the wording on the selection screen which indicates you’ll get something different to what’s in the chest’s description.