When you double-click, say, the word "double-click", do you expect to highlight either "double" or "click", depending on which part of the word I happened to click on? Or do you expect to highlight the entire compound? Does your expectation change when the phrase is written with spacing: "double click"? When written without spacing: "doubleclick"? Does your perception of the word boundaries change between these cases?

Now consider another anglophone arbitrarily; how likely does it seem to you that they would share the exact same set of expectations of the above with you? Because if they don't, then one of you is going to have their expectations violated.

Now give it a try: do the highlights match your expectations? (Moreover: are those expectations consistent with where you placed the word boundaries?)

If your expectations of what double-click highlight does for English is consistent with what actually happens when you double-click, it is deeply unlikely that the causality goes word boundary -> highlight expectation; if they do, it's more likely that double-click highlight has influenced your sense of word boundaries.

But it's even more likely that you your expectations of double-click highlight don't actually match up with your intuition for word boundaries, and you just have a pretty good model of how double-click highlight behaves independently of where you think the word boundaries are.

(The notion of word boundaries in this context is fraught anyway. Even setting aside the problem of compound words, the phonological word boundaries of Japanese don't match up with the lexicographical ones, in both directions.)