There are indeed detached cottages in existence.
But nothing like as many as there are workers' cottages in terraced form.
When the term was introduced (whenever that was), that was probably more or less the only form of the cottage. On that, I agree with you.
But that was then and this is now (or rather, it was a later time, at least, than "then"). The heyday of the terraced cottage was the second half of the C19 and the earlier part of C20. In villages such as this one, one will often encounter a row of terraced houses (usually more than three and no more than about ten) with the overall name "Xxxxxx Cottages" (and often a C19 building date on a plaque). There are at least four such locations I can think of within a half-mile of here. They're really not very different from the "Coronation Street" type of dwelling, except for the fact that sometimes, they are at right angles to the nearest road and reachable only on foot.