It is a self-diagnostic test that has been made along the CEFR (Sefaru), which is a criteria that have been internationally trust.
When you press the level diagnostic test, because the question that is in accordance with the level comes out, YES, please answer NO. It does not matter when you start from a level above those who are confident in English.
B1 may seem quite high but, for example, looking at the Junior European Language Portfolio it is a level considered attainable by elementary students in the UK studying a foreign language. You can attain it by putting the necessary effort!