2005 Tundra Double Cab - Coolant and Sparkplugs

I just had my truck sputter and run real rough friday morning on the
way to work. I wasn't sure if I was going to make it to the
destination. I took it into Maita Toyota here in Sacramento. They kept
it overnight and then told me the next day that somehow, mysteriously,
coolant had made its way into the 8th cyclinder's spark plug. They said
they have no idea how it got there and that they cleaned it out, and
performed a compression check and everything seems fine. Then the
service advisor said 'If it happens again, bring it back". That does
inspire too much confidence on my part. I only have 11500 miles on it,
and its only 6 months old. Has anyone had this problem yet with the
2005 Tundra? Any idea's on what it could be?

Mike.