That's really broadening the term 'irrational.' Irrational is not synonym for 'not good' or 'not preferred,' it just means not rational or not logical. There may be lots of rational choices, some of which may be better or worse than others - but all rational. Irrational MIGHT BE (loosely) short for 'that doesn't make sense,' or better, 'that's not logical.'
The bucket analog as illustrated seems to me more pointing at a faulty basis than irrational thinking. The budding author clearly linked spelling with being allowed to pursue writing that ends up in a successful career, and he has a point. An author cannot be successful without an audience; a piece where one continually has to stop and interpret badly spelled words is likely not going to have a good audience. There is a clear rationale. The faulty basis is more related to the student having a picture of being a successful author (1) at this stage in life, and (2) without discipline and development. The false basis in the picture is linking 'am I allowed to pursue writing ambition' with misspelling a word.