Lotto aren't asking from Ewan to win TdF sprints, that's absolutely not the point. They simply ask he keeps sprinting till the line when he can get a UCI points result, and don't let go so he gets swarmed by 20+ riders, scoring no points at all.
And this is the TdF. Just look at what riders like Petit did yesterday: a huge bleeding gap in their leg, they grit their teeth and they don't give up. Ewan voluntarily gave up in the biggest race of the year when the team most expects him to get points (there still were 3 sprinting chances in the last week of the Tour. All of those are waisted now.), but he made the choice to DNS as he knows he will get his paycheck anyway. Ewan didn't even inform Jasper De Buyst of his DNS: De Buyst rode his a.. off the day before, and looked like he was caught off-guard being interviewed at the start of the Saturday stage and being informed that Ewan wouldn't start. Every DS (and team mate) would be seriously annoyed actions like this.
What is left for Lotto vs Ewan the rest of the season? Lotto wants the points, Ewan wants...? With the mountaineous Vuelta, I think another GT is out of the question. Smaller one-day races? It seems like Ewan has had a year too much at Lotto.
Ewan abandoned during stage 13, it wasn't a DNS. So I don't know what you mean with the De Buyst interview.