No offence, Smola.
Mediocre is to mean, the average for Brit applicants who have been exclusively exposed to English throughout their lives. The test looks for the recognition of minute implications in a piece of text. I was told many Brits fail this test.
I think it would be reasonable for the assessors to make a bit of an allowance for the fact you are (very) fluent in more than one language; a useful thing.