Eric guarded the Block 1 street in between Zone 3 and Zone 4. The Block 1 street where he rescued the survivors was in between Zone 2 and Zone 3. Hence, he had to face a zombie horde coming from three streets.
Thankfully, the street behind him did not possess a single zombie. Aside from tasking Samantha and Jasper to finally start the production of the Evolution Crystal-Powered Water Purifier, he ordered them that once they hit a bottleneck or take a break an hour later, they must check the intersection on the other side.
Thankfully, they did not fail him. The rescue occurred near him either, so even if there was a zombie on the other intersection, it would still take quite a long time to notice the commotion.