why use camelCase naming convention when php defaults don't use it?

I see many software using camelCase for class methods: $this->classMethod();
But when they have to use a php's default method, it's for example : $resource->fetch_array(); (Not $resource->fetchArray())

Why use two different name conventions? Why not stick with the defaults?

 

There is no "default" for PHP. PHP is a random mashup of every conceivable naming-convention you can think of (and probably some you can't), so use whatever you think is best. One argument FOR using camelcase is that then you won't possible clash with already established built-in function-names (but, again, this is no guarantee).

 

So you don't end up mixing the two and can differentiate between php defaults and written by a coder.
Naming conventions are just for redability purposes. Makes your code more readable. Its not a parsing rule or something...