They make you take a breath test during the field tests these days. So you can do okay on the physical tests and fail the breath test.
You can fail the breath test for lots of reasons, poor pulmonary function being just one of them.
Unless he drank a lot just before leaving (it takes 45 minutes to absorb it fully) he might have been better off requesting a blood test. Breath testing devices can read high for physiological reasons and assume a standard relationship between blood alcohol levels and the amount of ethanol in alveolar air. That actual ratio can vary in humans by a factor of five or more. The blood test is generally more accurate.
That said, I have known people who were amazingly functional at BAC levels well above .15, not that I would necessarily want to share the road with them.
Me? I no longer drink, quit over 20 years ago.