[Some of] the tiny water droplets are nearly instantaneously being vaporized by the heat of the matchstick burning, causing a sharp increase in pressure in the air around the aforementioned droplets' locations, causing multiple mini "explosions".

Grab a candle, get some very thin wire and make a handle with a small 3/16" hoop at the end, and alternate dipping that inside water and molten candle wax. Sometimes it'll pop/sparkle (water), sometimes it'll burn (wax)...