Replying to Police entered my friends house

   We were chillin at my friends house, we were prolly about 15 person. sometimes people'd go smoke outside. At some point there was a guy showing me a magic trick, so i couldnt see the glass door. Then some guy yelled police! When i turned back my friend was being dragged outside by the arm. He argued with them for a while. They said that they received a complaint about people chillin outside (in french flanage). They seized my friend's pot (about 10 grams) and scheduled a court date for possesion.
Basically they said he was in infraction.
   at first, the police was just coming to see what was happening inside, but they saw through the window that my friend was  rolling a joint and just entered and seized it.
   Other guys that were there said that the police couldnt do that, that they couldnt enter someone's property without a warrant, or that they had to knock at the door and wait for someone to open before entering the house.

I didnt have an opinion on this, but why come seize a small amount of pot when you had a complaint about people chillin outside?

What do you guys think? who was in infraction knowing that this happened in Quebec.