As far as we are aware, he wasn't particularly knowledgeable in subjects that escaped the sphere of music.

In 1856, Eduard Mönike published a novella titled Mozart auf der Reise nach Prag or Mozart on the way to Prague. In the book, he writes a passage that I will translate here.

(...) Mozart never neglected an invitation to a party, meeting or stroll. A musical evening already habitual each Sunday at his home, a gathering of friends or acquainted around his splendid table twice of thrice a week, were obligations he did not know how to renounce. (...) The friendly laggard of a sparkling spirit, with his jokes and anecdotes, not always in good taste, was to him, as welcome as the most refined specialist or the most delicate musician. Mozart would often find the best entertainment outside of his home. You could see him each nite at the billiards, at the café and sometimes at the inn. (...) These diversions, sometimes brilliant and rampant, sometimes subjected to a certain quietude, would calm his constantly tense spirit (...) However, by siping up to the last drop of these momentary charms, he neglected everything else: commitments and reading, formality and economy. In enjoyment and in creation, Mozart knew no limits. (...)"

But aquatermain, why on Earth are you quoting a novella? You may rightfully ask. Because, ignoring the poetic licenses behind the prose, and the embellishments, and the obvious fictional elements within the book, there is some truth.

According to basically every historiographical work I've read about him (excluding the strictly musicological ones, because those care very little about his personal life), Mozart was not very good at managing money. Abert Hermann (Wolfgang Amadeus Mozart: eine Biographie), Alfred Einstein (Mozart. His Character, His Work), Eduardo Rescigno (Wolfgang Amadeus Mozart [compilation]) among many others, agree upon his constant mismanaging and extensive spending, and they tend to attribute it to his hedonism. When he had money, he would spend it in luxury items, clothing, food and drink, and in "going out", which consisted in constantly attending social gatherings in the different cities he lived in. When he ran out of money, he would depend on loans and the charity of his friends and acquaintances, as well as his patrons. There are several examples in his letters that illustrate his financial troubles, the most notable of them written to fellow Mason Michael Buchberg, claiming that “(…) should you, my best friend and brother, desert me, I shall be exceedingly unhappy and innocently doomed with my poor sick wife and child (...)”

How does this relate to your question, then? Well, we've seen that a considerable portion of his resources and time were spent in enjoyment and social activities, while the rest were invested in music: composing, teaching and performing. Rescigno, citing Luigi Ronga's Bach, Mozart, Beethoven. Three Critical Problems, explains that Mozart was a practitioner of the cult of perfectionism. As such, he compares Mozart's compositional style with Beethoven's, stating that Beethoven believed form to be the fruit of a constant fight of different structures and ideas, and therefore, he left behind hundreds of scribbles and drafts that eventually led to his idea of the perfect form for a specific composition. Au contraire, Mozart left no traces of corrections or modifications and, even in those works he left unfinished, looking at the score, even if incomplete, one can appreciate the perfectness of his form. Furthermore, he states that Mozart's love for perfection equated to a conceptualization of art not just as an expression of feeling, but as professional skill.

If we take these ideas into consideration, if we look at a composer who defended the idea that being an artist meant a high degree of skill and professionalization; a man who devoted the majority of his days to perfecting and honing said skills, while spending what little time he had left between studying and work, to enjoyment and the hedonistic pursuit of fun and pleasure, there is little to no evidence to suggest he had a big interest in the idea of being a polymath.