Part of sportsmanship is the agreement that both sides want to do as well as possible. In individual game results, overall arena performances, and rating performances.
If you are intentionally playing moves when you could just let the game get aborted, you are not playing for the best rating, which in my book is unsportsmanlike. You may disagree with this definition, but I have no problem with my opponent stalling out the end of the arena. When you start a game late in an arena, you and your opponent should both know that you need to play quickly, or else any advantage gained is for nothing.
Imagine using Hikaru as an example of good sportsmanship.
Running the clock out at any point is unsportsmanlike. Just because it's the last few minutes of an Arena match doesn't make it any less so. What if the person on the other side of the board is a contender for first place? Just because you're a sore loser, they shouldn't get a chance at their points?
Running the clock out egregiously at any point in an Arena should be punished heavier than a regular game. Had a guy in a 5 min Blitz game run 3 mins out yesterday, moving me from 2nd to 10th as the other people in the top ranks won games while I sat there twiddling my thumbs.