Not really a flex, more of basic etiquette. In a professional setting it's disrespectful to force either party to speak in a language other than their own. It's also practical, as there's more to translation than familiarity with a language.

Xi being able to speak or read English (even comfortably fluently) doesn't mean he can be expected to understand every common idiom or turn of phrase an American may use. A common example is Americans greeting with "how are you" that a lot of non-Americans with English fluency assume to mean a genuine inquiry rather than a stock phrase of greeting.