You're assuming 1 gallon of fuel consumed by a pickup truck emits the same amount as that emitted by a 2-stroke leaf blower engine consuming 1 gallon of fuel. They definitely don't.
I link some sources in a separate comment up-thread, but the short answer is two stroke engines run orders of magnitude "dirtier" than a four stroke in a car, primarily due to incomplete combustion of fuel. (Some of this is fundamental to the physics of their operation, and some of this is they aren't subject to the same strict automotive emissions standards, so less engineering goes into reducing their emissions)
Intuitively, this is why you can sometimes taste a lawnmower running the next block over in the air, but the same isn't true for a modern car idling, even if they were consuming fuel at the same rate.