A sect is a sub-group of people unified by beliefs or practice, a denomination is essentially just a large named sect. Christianity is not monolithic and organises into groups, it by definition has sects.

Even if you were right it's such a ridiculously pointless and pedantic argument, it does nothing to further the conversation. You're just trying to use cheap gotchas as a thought-terminating cliche. The only thing you've done is to force us to literally argue semantics, that is not a good look for you.

For completeness, here's a Christian source using the word sect to describe Christian groups, one of the top search engine hits when I searched.