You can use either Hosen (plural) or Hose (singular) here. Is Hose also a pluralised word on its own, like pants and trousers? In that case, what's the point of having Hosen if you'd just use Hose anyway...? Would you use it in the context of many people, like "Ihre Hosen" meaning "their (multiple pairs of) pants"? German is much more logical than English, and yet it's still so confusing.
I'd like to know whether there are linguistic terms for these kinds of words that are grammatically singular but actually mean a pair (or more) of something. For example: Die Hose (sing. trousers) - Die Schuhe (pl. shoes)
For your question and this is a direct quote from Wiktionary: "In contemporary usage, the plural Hosen is typically used only for several pairs of trousers. However, it may also be used interchangeably with the singular. Thus, er trägt eine blaue Hose (“he’s wearing blue trousers”), or dated, er trägt blaue Hosen."
I'm not sure whether this (historical) reasoning works for German too: https://www.britannica.com/story/why-do-we-say-a-pair-of-pants