Call non-statistical class methods without instantiating this class

The other day I started to "refactor" a PHP program with the goal of screwing it to the PHPUnit working code. In the process, we had to rewrite the class with statistical methods, replacing them with non-statistical ones. Logically, after this change, the prog was supposed to fall in every place where these statistical methods were called. But this did not happen; not only that, everything continues to work correctly:

  class MyClass1{ public function foo(){ print 'foo'; } } class MyClass2{ public function printFoo(){ MyClass1::foo(); } } 

The foo() function in MyClass1 was previously declared statistical, but deleting the "static" keyword from the function declaration did not affect the operation of the program either. This is normal? Why does this work?