The speaker is surprised to see the dog, the doily, and the plants at the filling station. All are signs of domestic tranquility.
The filling station is a very utilitarian operation. The family that owns it seems to live there. There are some signs of the family’s softness that do not belong at a filling station.
First of all, there is a dog.
on the wicker sofa
a dirty dog, quite comfy. (poemhunter)
The dog is a sign of domestic tranquility because it is a common household sight, it is on a couch on the porch, and it is “comfy” and therefore pretty happy. In a businesslike, dirty place, the dirty dog is an anomaly.
Next, there are the plants and the doily.
Somebody embroidered the doily.
Somebody waters the plant,
or oils it, maybe. (poemhunter)
The speaker is surprised to see plants and a doily, signs of household bliss and comfort. Somebody takes the time to do these things. This is how the speaker determines that “Somebody loves us all.”
This use of “somebody” in describing the wife or mother can be taken too ways. You could say it means that we all need someone to take care of us, and the mother represents all mothers, or that the mother is anonymous because she is insignificant because the men dominate that filling station.