Hi and welcome to the Netherlands! (I'm Dutch myself)
Usually when someone greets you with a simple "hi" (or a similarly short greeting) it means that they're just being friendly, but are not looking to start a conversation.
When the greeting has a follow up (usually a question) it often indicates that this person is interested in a conversation. For example something like:
Hey, how are you doing?
The same applies when you want to start a conversation yourself. When someone replies to your question with just a short answer, it usually means they're not interested in a conversation. Otherwise they'll just tell you they're not interested (don't have time).
And like WordsandNumbers said, don't be afraid to ask. Especially your friends/acquaintances, they'll probably understand.
Also, please note that Dutch people can be quite direct when talking to you. It might come across as rude, but it's just the way we are.