I have been able to recreate the problem you are having locally and as that other post says Sitecore Forms logic is indeed weird!
As that post states, it looks at each condition in order and if its true applies your action, but if not it applies the inverse of the action. The last action to influence an objects state is the one that is applied.
In your case, because you want to hide both sections if radio is empty, you need that to be the last condition (otherwise the other radio conditions would make one of the section show if applied after). The problem is though... by adding that condition as last condition, when it is not true (i.e. radio selected) the INVERSE is applied last - so both are set to show.
I dont believe it is therefore possible to add a set of conditions to achieve your goal, based on the current layout of your page.
My suggestion would be to add an invisible parent section, that surrounds the other two sections. Then apply a single condition referencing that. So if radio is empty, hide the parent section.
You can then apply a further condition, stating if radio is equal to "Credit Union", show/hide sections within the parent. Note, due to the fact the inverse will be applied if NOT true, you only need the one condition adding, because if it is not equal to "Credit Union" then the inverse is to hide credit union and show organization name section.
Hopefully the screenshot below shows what I mean.