Riddle me this. Riddle me that. BACKFIRE?

[spldart]

Had the bike for a few thousand miles now.
Today i left work and got 4 miles down the freeway and I let the throttle down,
not off just down, and got a backfire out the exhaust.
First and only backfire.
Bike ran another 20 miles normal power, normal idle, normal start.
Heck. I just ran back to grocer store to hit redbox and grab a couple dvd's and
back home. Perfect operation.

I have been doing constant checks on compression and reading the plug.
Plug read says my mixture is great.
My mileage is mid 70's so yeah. Running good.
Got it back to easy start except when it's insane hot out. But otherwise it always
turns over less than a second.
Factory exhaust and I haven't disturbed it.
Bolts at exhaust/head are still tight and i don't hear a leak.

I'd understand if i had disturbed the exhaust and not used a fresh gasket.
I'd understand if I was having mixture issues.
But an engine that runs and starts great belting out a serious one time only
bark?

Any thoughts?

"edit" i run middle octane gas. Just because it's so hot and higher octane resists predetonation better.
I'm not running premium however. Just one step above the cheap stuff.