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The SERPS on the for 'Y' show the variation of the KW (X, ,widgetion, widgeters) bolded. But no 'Y' on the SERPs page. If the search is done again for Y in quotes the SERPs will contain pages that have Y in them.
So google is not really returning results for Y when searched, because those results do exist. And the results they do show are not exactly the same as the SERPs for X. So they are not those either.
What is Google showing for the results when you see did you mean...
It is to keep the idiots happy who cant type the word widgte
It is basically showing you how ignorant you are and being a pedant about spelling