... that a "cottage" was just a name given to a genteel house by someone who has a larger house to compare it to! And that it didn't really have any particular features, other than being smaller than something else (though it might have been very large indeed).

Thanks, BarbaraB, for the reminder about Charles and Mary Musgrove living in Uppercross Cottage, which had been "elevated" from a farmhouse. I would imagine the elevation involved a few minor renovations to make it more suitable for the gentry, topped off by the new name to make it more fashionable.