Pete, anyone can lose a player to Barcelona/Real Madrid. Doesn't matter how big you are, those two can prize anyone away from anybody.
Dembele, Ronaldo, Bale,
Now I wouldn't class Dortmund, United or Spurs selling clubs, yet they've lost players (very good players) to those clubs. Players they would of liked to keep. So did we.
So no, I don't class that as a selling club mentality. What I do class as a selling club is when clubs sell players to clubs who are their direct rivals, because in that scenario you should be able to offer similar benefits as said rival: Salary, chance of silverware, exposure all that stuff. There shouldn't be a reason why a player would want to leave club X for club Y when they're competing for the same stuff.
But if that situation does happen too often, then yeah I'd consider that a selling club.
Now that's just my interpretation of it though. I don't know if that's correct.