Some people over-explain when they speak, loading up details and numbers and explanations into every sentence. But other speakers have the opposite problem, pulling their punches and under-explaining, offering few facts and absolutely no embellishment.
I found myself doing just that when I was first learning to handle media interviews. I’d been a reporter and knew too much about how statements might get taken out of context, so my answers were terse at best. The trainer took me aside and said, “I almost never say this to anyone I’m training, but you need to say more.”