Exactly. SQS is a queue where a message resides. Lambda basically polls this message. But like kondro said basically it doesn't matter (directly). I think it is important to understand the event source mapping takes over the polling. But in the end it looks like a push system.

But the whole point about costs with empty queues is important. It is definitely important to understand if you want to customize queues for example with long polling. This parameter changes the time your lambda will poll from your queue