Is it possible for a new oil delivery to cause problems?

About a week after my oil fired boiler was serviced the chimney was belching black smoke. Engineer asked if we'd had a new delivery of oil, which we had, and he said it had probably stirred up all the gunk in the bottom of the tank and cause the black smoke. The filter was clean but the nozzle was gunked up and he had to replace it and practically re-service it, taking 2 hours in all. Is it possible for gunk to get to the nozzle without going through the filter?