Having looked at several websites I see purée does mean mashed potato in the absence of any other context. I suppose in the same way we say e.g. pie and mash or bangers and mash without specifying potatoes.
Don't know where you are looking but in nearly forty years of visiting France I have only ever seen mashed potato written as pommes de terre écrasée. A puree is a different thing, incorporating butter or cream to make a smoother, thinner mix.