A useful picture for this word: something turns up looking as if it belongs, and then cannot show where it came from. An argument arrives sounding well supported, and the support is not there. A smile arrives looking like sympathy, and no feeling is behind it. A line arrives on a scan looking like part of the body, and the machine made it. Each time the surface is convincing and the origin does not check out.
From the word’s history
Wiktionary gives the word as a borrowing of Late Latin spurius, meaning illegitimate. That old sense is about a child who could not point to a recognised father, which is the same shape as the modern uses: the thing is present, but its origin will not stand up.
字典記載 spurious 借自晚期拉丁文 spurius，原意是「私生的」。那個舊意思講的是一個孩子指不出被承認的來歷。今天的用法還是同一個形狀：東西就在那裡，來源卻站不住。這條線索可以當記憶的掛鉤，不必當成每個現代用法的直接歷史來源。
Wiktionary, "spurious"
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