This probably happens because Word uses language settings for a language that uses “chevrons” (double angle quotation marks) as quotation marks, such as French. By default, Word auto-corrects Ascii quotation marks (") to language-specific marks, e.g. to “smart” curly quotes for English. The fix is to change the language setting (click on the language indicator for this). It won’t change the quotes already entered, so you need to fix them separately.
By default, Word uses language guessing: it tries to infer the language of text from the text itself. It sometimes guesses wrong. I don’t see why this would have happened here, as the text looks like normal English. But maybe the language setting was originally e.g. French and language guessing was off?
It’s odd that Word uses «gains», because by French rules, the quotation marks should be separated from the word with fine spaces. The Windows versions of Word therefore insert normal spaces: « gains ». This isn’t quite correct, as the spaces should be fine, narrower, and maybe the Mac version therefore doesn’t introduce the spaces. Or maybe it is applying the rules of some language that uses chevrons without spaces.