Is bbq smoke carcinogenic? left window wide open and neighbours having bbq right below and filled the room very badly. will this cause third hand smoke like cigarette smoke does? is it as bad as eating the burnt food? also fan was on right by window?

You should enjoy life, do not concern much about that little nuisance.

The incident you described will not change your inherent risk of cancer. You can reduce your risk of cancer by adopting healthy habits: Eat a mostly vegetarian diet, avoid alcohol, tobacco and street drugs, avoid excessive exposure to sun, maintain healthy weight, get HPV vaccine, exercise 30 minutes each day, drink enough water so your urine is mostly colorless. Wish you good health!