It may or may not be meant as an insult. Depends on how it's used, by who, and to who.
Most 'natives' or locals say howlie to make white people feel bad or guilty or intimidated to be on 'their' land
Most people with Hawaiian decent are really cool and not all use the term Howlie on the whites.
Is your called a Howlie....just ignore it.
It is the equivalent of the black term "cracker"
Hawaiian Nattive 2: One of those damn Howlies. I think he was from Vegas or something.