If I had to guess, based on your picture, I'd say your wood chunk was not burning clean (too much smoke), and you cooked with the lid on. Most pizza specific accessories have massive openings, to allow high heat and smoke to vent out. Next round, try just using the lump, with no wood chunks. The lump will most likely add a nice flavor to your crust
Do you all normally use any flavor wood when you grill pizza?
Yes (mostly oak), but I use a Kettle Pizza 100% of the time for pizza.