Psychology help on memory?

I would say selective attention. The server isn't taking in a lot information to be used for later. He/she's mind is specifically focusing in on key words and phrases, like "I'll have a ....". Once the information of the order is given and the server has it in their mind they will then encode the rest of the information like conversation. If you ask the server the first detail of what they remember about the customer odds are the first thing they remember is what they ordered.