How do we know if the words tha e is: he is or it is?
From context. It can be both.
In Scotland you wouldn't call a person short, you would say small, so I have a feeling that a person would not be goirid, but beag. Maybe you know more about this - it is not a question of what you say in American but in Gaelic.
In Scotland, you definitely would call someone short. Short and small, when referring to a person, aren't always synonymous.