An easy way, which is at least mostly true, to remember the use of assumption versus presumption is implied negativity. Presumption being the negative version.
We live in a presumptuous society.
All day people jump to conclusions, often based on no information at all, about others. I doubt this is intentional. It may be an evolutionary trait, designed to filter out “unnecessary information.” A world based on written as a posed to spoken communication doesn’t help. It is notoriously difficult to read emotions in text.
Either way, it is dangerous and often leads to a confrontation in some cases, and regression in others.
In the same vein, if you believe someone else to be presumptuous, for whatever reason, best you pause and check your own reactions, chances are you too are behaving presumptively.