An "expert" is someone who has deep knowledge about something. For example, an expert in economics is someone who has studied economics for many years, and may have written books or taught classes on it.

When you use the phrase "some kind of expert", it seems like you have doubt about whether someone is really an expert. Imagine that your sister tries to give you advice on how to save money. You're annoyed that she's trying to give you advice, because you think that you know more about money than her. You can say this sarcastically:

Oh, are you some kind of expert in economics now?

Some other examples:

He tries to act like he's some kind of technology expert. Whatever!

It's annoying when people study something for a few weeks and then they try to act like they're some kind of expert.