I hope you can help me clarifying. I've watched this video that explains the difference between "Will" and "Going to" (with referring to future plans specifically). With reference to such video the teacher says the use of "Will" is bounded to instant decision, while "Going to" is used to refer a future planned before the moment of speech. The examples made however are in positive, for example it covers case like
I'm going to eat out this evening
which means that in the future I'll eat out, but that such event has been previously planned. While
I'll eat out this evening
means that in this moment I'm kind of planning my future. It makes perfectly sense to me that the meaning of
I won't eat out this evening
means that I'm planning now to don't eat out, but what about
I'm not going to eat out this evening
Is this suppose to suggest in general that I have other plans for the evening?