To be precise, the music box just barely reached high-tier, but it still went above the standard line that separated it from items of lower ranks.
Angor thought his alchemy works would only reach this level after he turned a wizard because as commonly believed by all alchemists, making a true high-tier item asked for many aspects not bypassable by using extra help, such as the maker's own power level and how many advanced alchemy spells they could use. Right now, Angor met none of these conditions.
However, there were known exceptions that fell out of these limits. These exceptional creations had such strong effects from the very start that they were not limited by poor materials and incompetent techniques used by the alchemist.
Commonly, alchemists needed to rely on high-level materials and skills to ensure a better outcome because items created in such a way wouldn't turn out so badly even if they made some minor mistakes in the process.