The only rationale I can see for INT here is to claim that the fielder is still in the act of fielding a batted ball, rather than recovering a misplayed ball, and thus still protected.
So I suspect that the crew ruled INT because the fielder kept the ball in front of him. Had a misplayed ball gotten behind F4 (playing in?) and taken him into the runner's path, likely that would be ruled OBS.
Either that or they booted the call.
