From the Cambridge dictionary:
Used to describe an employee who deals directly with customers, or who
is directly involved in making a product
So as a "code monkey" (Makes a product) and someone who sometimes interacts with customers, you are considered a front lineworker by this definition.
Generally frontline workers are those who know what the customer is doing and are either interacting with them directly or via a third party E.g. a piece of software.
A frontline worker can report on how the customer is doing and what actions they've done recently, wether this being done via talking and interacting with the customer or interacting with a product that a customer uses.
A developer can be considered further frontline as they are often third line support and will need to communicate with a customer, from time to time. They are also often bought into technical design meetings to confirm that what the customer wants is possible. Regularly during a sales meeting, I often find we are talking with a "suit" and a developer. One to deal with the business requirements and the other to deal with the technical requirements.
The only time this isn't the case, for developers, is if you are working in an environment where you are just used to churn out code. Then you tend to only have requirements provided by managers and never interact with the end user. So it does depend a little bit on your company's philosophy. However, you did mention you have met customers, so it would be safe to assume you can be considered frontline in this case.