Remove the rubber boot. Is it clean or covered in filament? My guess is, as others have said, the nozzle is loose. It should not be snug against the block but against the other feed pipe. If filament oozes out the sides of the threads, it might get pushed around the inside of the boot and come out the holes in the top.
It was likely a loose nozzle that wasn’t properly heat tightened.
For those who don’t know, after screwing the nozzle in cold, crank the hotend up to max (or hotter than you ever plan to print by about 10C) and tighten the nozzle again. The thermal expansion is different between an aluminum heat block and a brass nozzle. The extra tightening while hot can overcome this problem.
Remove the rubber boot. Is it clean or covered in filament? My guess is, as others have said, the nozzle is loose. It should not be snug against the block but against the other feed pipe. If filament oozes out the sides of the threads, it might get pushed around the inside of the boot and come out the holes in the top.
It was likely a loose nozzle that wasn’t properly heat tightened.
For those who don’t know, after screwing the nozzle in cold, crank the hotend up to max (or hotter than you ever plan to print by about 10C) and tighten the nozzle again. The thermal expansion is different between an aluminum heat block and a brass nozzle. The extra tightening while hot can overcome this problem.