It most certainly is a "ping" test. It can only obtain the maximum speed that your ISP provides. - possibly at that particular time of day, accortding to the traffic volume on the ISP. Any server you test, with the program, will give you the same results, as will any browser.You can check this by selecting the lower option on the site "My Results".
You can also test the quality with the middle Windows "Ping test.net" Nowhere does it refer to a particular browser.
The blurb, which is country language specific, says "First test your connection, Get a fast Web browser afterwards". The recommendation, is a spammed "Chrome"
You can also go to the right of the page, and select the option to "Test your Connection". This will lead you, eventually, to the offer of several uniblue products to improve your computer.