It depends which one you mean. I didn't watch any of matches in Roland Garros this year, except yesterdays Djokovic vs. Federer, so I might be wrong. During this match I saw quite few just next to court in first line. These were photographers for sure, since this is normally place where we can be. But why it looked like they are following game as spectators and not shoot? Simply... match went on for almost 4 hours. You need 20 or 30 photos from match, and celebration photo on end. So you are trying to kill those 4 hours there, since you get all the photos you need in first 10 or 15mins already. That's reason why tennis is most boring sport to shoot for me.
If you meant others then those, then I would need some more info where exactly they were There are other positions around the court too, and normally you can go almost anywhere on tribune, so it could also be that. Or there could be just normal spectators who were allowed to bring bigger lenses in. I have no idea what's policy about this in Roland Garros... or anywhere else in matter of fact