After a WOT run of third gear for giggles tonight, which I lifted from at only ~6k rpm, there was a small backfire and I see behind me what appears to be fireflies swirling. A few sparks hit the ground, others just floated and disappeared.

My car is a single turbo, all emissions removed and a straight pipe to a Greddy Evo cat back. Car ran and idled fine afterwards. I've never noticed flames, but I understand it is obviously fairly common (and most likely happening regularly), but sparks sorta made me sit up and pay attention to my gauges; all of which read within normal ranges aside from the unreliable knock sensor readout on the Power FC which read 106.

Is this something that is cause for alarm or simply a random chance event of carbon buildup within the exhaust breaking free in an attempt to start a forest fire?