The event with your mother doesn't necessarily have to have such profound meaning, not to say that it couldn't be strange logic. What I mean, though, is it probably has very little to do with some bizarre logical process of her expecting you to help her regardless of dismissing your offers to help, and probably shouldn't be assessed for being logic in the first place unless she stated it in a way to suggest it as such (something like, "When I said I didn't need help, you were supposed to know that meant that I needed help."). It may just have to do with how her mind works, and doesn't.
For example, my father took me to pick up fast food to take home last Wednesday night, and we do this almost every Wednesday night. There was a huge soda spill at the counter, so the employees were rushing to clean it up, so they were understandably distracted. We got the order after a little longer a wait, got back to my place where he noticed there was no sauce for the chicken strips he had ordered. He held a rather judging tone and assessed their incompetence of having not given him the sauce he had asked for when they asked him what kind of sauce he wanted. I was there, they were too distracted and forgot to ask, and he never asked himself... he must have remembered asking for the buffalo sauce he asked for the week prior, but was certain that moment a full week ago was only fifteen minutes prior. Just for context, he's in his early fifties(becoming rather forgetful), and it doesn't seem to help anyone's patience/irritability levels or cognitive ability when one hasn't eaten for a while like neither of us had, and it was rather late in the evening for him at that point. That doesn't make excuse for his unpleasant attitude, but it does make his behavior make sense to take in all of the context of the situation and let it slide... Which seems better for my peace of mind and his rather than expecting constant perfect behavior to shine through human frailty, and to judge for when it does not.
It's completely possible your mother was so distracted she shrugged off your offers of help without really thinking, and then wondered why your help never came... kind of like how it's possible to eat a whole meal while watching a favorite show and then wonder where the food went if not mindful to taste the food. It's maybe also possible she was tired, hungry, and as consequence cranky after having done such work and made the mistake of speaking poorly chosen words at the sight of your relaxed state.