>Those two dots, often mistaken for an umlaut

Hmm maybe it's because it looks exactly like an umlaut and is often placed exactly where an umlaut would be placed?

The diaeresis and umlaut are literally exactly the same Unicode character and the symbol or diacritic itself can be called either. The difference is what it does to the vowel — it’s a diaeresis if it indicates a repeated vowel, and an umlaut if it modifies the vowel sound.

Just to note, a diaeresis isn't always the same vowel repeated. The most common example is "naïve", and it also occurs in names like Chloë.

Whoops, you’re right, my explanation missed that!