No, it wasn’t wrong because it didn’t specify which average was meant. If it was “arithmetic average”, it would be wrong.
It would still be right. The test results are reported on a normalized curve so all measures of central tendency are all equal.
If you don’t specify then the statement needs to hold for all averages to be correct.
“I have a ball”
“So you have a red ball?”
“No, it’s green”
“If you don’t specify then the statement needs to hold for all balls to be correct.”
And by the way: for the given plot, it is correct for all averages
More like
“Balls are orange”
“That’s wrong”
“Ah but basketballs are balls and they are orange, gotcha”
“No, you just said balls, that’s too generic, if you meant basket balls you should have said basket balls.”