He basically says you should always put your sunscreen on as your first layer, before any makeup.
Throughout the day, generally things applied to the skin fade off as the day progresses, with sweat and skin and movement, which is why you usually want to keep reapplying your sunscreen.
If your makeup fades throughout your day, then chances are your SPF has faded too, so you'll want to reapply both regardless.
If your makeup looks just like new, and hasn't budged, then chances are the layers underneath (e.g. your sunscreen that was your base layer) should still be in place as well, so you shouldn't have to reapply your sunscreen and still be okay.