Translation:The artist is explaining that he rarely buys expensive clothes.
I understand you meant "singular they"? Well, Duolingo has no way of knowing you meant that and not making a big grammatical mistake. I've actually already written you an answer about how you changed the grammatical number for no reason, before suddenly understanding that was probably not the case. So personally I think it's safer not to accept 'they' and just go with 'he' or 'she', whichever you will choose.
Sorry, but you're wrong about this. It doesn't matter what the adverb modifies, 'rarely' is almost never placed in front of a pronoun, especially if it's after a conjunction. I suggest you read this:
The iweb corpus confirms that your suggested word order is 1100(!) times less common than our main translation.
I wonder why almost no one places 'rarely' between a conjunction and a pronoun in real life, but here everyone is suddenly strongly in favour of it... well, it's the Polish word order, isn't it? I think we solved the mystery.