They're interchangeable syntaxes. One is inherited from python, the other from Lua. In Godot, you can also access the keys of dictionaries like:
Thanks for the explanation!
I knew about the python way and the ".key" way but I didn't know about that one! It's fewer character to type, and characters where I don't have to hold down shift, so I might try to get used to this way!
You're welcome :)