An SPL test for earphones is usually done in an anechoic chamber in order to be precise, and accurate. Because the output hole is so small in an earbud, the testing device's transducer must be place right up next to the item being tested, without contacting it.
Thus any background noise would raise the noise floor and render the test results suspect. If your ears are ringing, damage has occurred. Whether it's permanent or not is another question.
Your statement of "meant to be 108db" is inaccurate. The 108db rating is probably what the device will output with an input @ a specified voltage input.