Just going by some industry reports I've seen, though since Apple doesn't release sales figures, it is hard to say. Of course, while the Apple X may have sold better since it has been released, the 8/Plus still had about a month and a half of sales prior to the X being released.
And this is ignoring how you can "play" with sales numbers. First, "top selling phone" likely is stating only that it has sold more than the 8 and more than the 8 Plus, not both combined. It also begs the question, though it sounds like he was saying units sold, "top selling" also could mean highest sales in dollars; where the 8 and 8 Plus would have to sell more units to equal the amount sold in dollars.