You also instantly knew what the person meant by a couple because this is an extremely common usage. Oxford agrees as well, if you use their US dictionary [1].

You also instantly knew what the person meant by a couple because this is an extremely common usage. Oxford agrees as well, if you use their US dictionary [1]. [1](https://en.oxforddictionaries.com/definition/us/couple https://en.oxforddictionaries.com/definition/us/couple)