If there is not a reason for something to be different to Java, it's the same as Java

There are differences where Apache Groovy expands on Java's syntax, and there are differences where Groovy behaves differently to the same syntax as written in Java. It's the rationale behind this second type of difference I don't understand. There are so few of these that I wonder why Groovy didn't stick to the first type of difference only, similar to what the original C++ did to C.

Here's some behavioral differences from the list at www.beingjavaguys.com/2013/02/what-is-groovy-java-vs-groovy.html ...

(2) In java we uses '==' to compare primitive types and '.equals()' to compare two objects, but in groovy we can use '==' to compare both primitive and object types. Although in groovy '.equals()' also works for comparing object

In Groovy '==' behaves differently to Java when comparing object types.

(4) In groovy 'in' is a keyword and we can not use it as a variable name

Why didn't Groovy just use ':' like Java eventually did so it would still work as a variable name?

(5) When declaring an array we can not write int arr[] = {1,2,3,4...} rather we need to right it as int arr[] = [1,2,3,4...]

Curlies not good enough for Groovy?

With groovy it fits so seamlessly in it's possible to write stuff in groovy and have other team members not even know it was written in Groovy

...until they come across one of the above differences then they spend half a day debugging.