When you're asked a question at a press conference, you're not obligated to answer. But it's how you answer that often speaks volumes.
When Golden State Warriors head coach Steve Kerr was asked earlier this week about relations between China, Hong Kong and the current protests, Kerr deflected the topic, admitting he wasn't well versed on the subject matter. He wasn't as shy later in the week after being the target of criticism from POTUS.
Being opinionated on issues inside our own borders doesn't mean you're speaking badly about America, as POTUS suggested. It does indicate that Kerr understands the enormity of speaking well and informed about issues which he's asked to provide an opinion.