You are getting your terms confused a little bit here. To put it simply, what you are describing is a private meeting between a priest and a member of the faithful. However, not every instance of a priest and a person privately discussing the discipline of the Church, the sacraments, Church teaching, etc. is an instance of "the internal forum". Read the following piece by Edward Peters to get some more background info:

https://canonlawblog.wordpress.com/2015/11/20/toward-informed-discussion-of-the-internal-forum/

Whether you use the internal or external forum in these situations you are still searching for a definitive judgement. In these cases the external forum has declared "there was a real bond of marriage". Folks on the AL side want the internal forum to be able to say "don't care what the tribunal said, we've reached an alternative decision, the marriage was invalid." Basically a private, mostly biased appeals court of 2-3 people declaring marriages null for convenience sake.