Yeah, that’s mostly true, but the front porch of a home is part of the home for 4th amendment purposes. Police obtaining warrant-less access to your front porch would violate this.
If someone is out on the street, it can still be illegal depending on the state. In new york, for example, the definition of illegal eavesdropping includes:
“Mechanical overhearing of a conversation” means the intentional overhearing or recording of a conversation or discussion, without the consent of at least one party thereto, by a person not present thereat, by means of any instrument, device or equipment.
There’s no no stipulation about location.
In this case, though, it probably wasn’t $3.80. That’s what the cost would have been to the owner of the gas station, but to the cashier, letting a customer walk with goods could cost them their job. Definitely a different risk/reward