> As in, the word "church" only refers to Christian places of worship.
That's not correct; e.g., the first definition from the full definitions at m-w.com is "a building for public and especially Christian worship".
In practice, there is more to it than that -- its not uncommon to be used generically and inclusively for place of worship, but you'd never (except through ignorance) use it for a specific place of worship except consistently with the usage of the group for whom it is a place of worship. (But the groups who use it specifically for their places of worhsip is also not the same as "Christian" -- it includes many, but not all, Christian groups as well as some, mostly newer, non-Christian groups.)
More relevant to the thread: the use of "church" doesn't seem to be about a place of worship, anyway, its about a body of believers, which is a use of the term which is somewhat less divisive, though still has the same generic for unspecified religions (though "congregation" would probably be better) and specific for some, mostly Christian, religions. So, its not an unreasonable single-word term to use in explaining the function of a generic product, though the complexities of the use and the emotional attachment that goes with naming issues around religion may make it problematic. Though, really, the name ("OneBody") of the product is far more of a specifically Christian reference than the word "church" in its description of purpose.
> Now, if you are saying that "church" means any Christian place of worship - as in, people don't differentiate between church and cathedral, which are different things
Well, this is far off the point of even this subthread, but the set of cathedrals is a proper subset of the set of churches in the way both terms are used by most groups that use the former term at all. That is a cathedral is a church that is also the seat of a bishop. So even outside of the generic sense, its proper to refer to a cathedral as a church.