This was bothering me, so I did a "Virgin Ears" test.
I had my family listen to the audio clip from Snopes without telling them ANY background whatsoever.
My dad thought it was saying "Gotta Light?" and my mom heard nothing.
Once I revealed the controversy, my mom then heard it, and my dad was still confused.

However I heard "Islam is the light" the first time.

I think someone interpreted it wrong, word spread, and when you are listening for it, you hear it.

Additionally, "Light" is the only distinct word. "Islam" is very garbled.