From what I’ve read it looks like the Convoy passed the “Safe house” on the way to Haman’s group, spent some time there, then went back. This probably happened pretty regular, and there are only so many roads you can take.
A good bet would be someone from the safe house saw them go down, ( on a motorcycle perhaps ? ) and went up to position himself if the convoy took that route going back. Might have repeated it a dozen times waiting for the chance. They would have known exactly the best place to be. The taxi spot was just about the worst place to be.