Question: Hello.
I don’t know if this situation is already illustrated on this blog,

Please, could you explain me why this decision was correct? And when the referee have to or haven’t to give a whistle signal to start free

Answer (March 31, 2013):
There is no need for the whistle on a free kick of this sort. You will find this information in the Laws of the Game, Interpretation of the Laws of the Game and Guidelines for Referees. Also note that I have added emphasis (bolding) in several of the points made.

The Laws of the Game tell us:
Use of whistle
The whistle is needed to:
• start play (1st, 2nd half), after a goal
• stop play
for a free kick or penalty kick
– if match is suspended or abandoned
– when a period of play has ended due to the expiration of time
• restart play at
– free kicks when the wall is ordered back the appropriate distance
– penalty kicks
• restart play after it has been stopped due to:
– the issue of a yellow or red card for misconduct
– injury
– substitution

The whistle is NOT needed
• to stop play for:
– a goal kick, corner kick or throw-in
– a goal
• to restart play from
a free kick, goal kick, corner kick, throw-in