>>Could be he had just used a popular brand of mouthwash.
Happens all the time. Makes headlines.<<
Don't know if it happens all the time but here's an earlier case involving breath mints:
http://www.pprune.org/forums/showthr...threadid=79661
Also, here's another case where it appears the test was negative:
http://www.pprune.org/forums/showthr...threadid=69849