This is an idiomatic expression because it's impossible for someone to literally be part camel. Camels are known for going long periods of time without drinking water, much longer than the average person could. So, we may tease someone for being "part camel" because they have gone a long time without getting something to drink and don't seem to need it. Maybe you heard someone say this after someone refused a drink?

If you are asking what "somebody is part camel" means, it means they can go a long time without drinking water.

It is often used as an insult