Full slinging in a casual game?

Just played a 17+ HD nomad game with some random players. The civ of the enemy team's best player was Berbers. Although we had water control, he went to imperial within 27 minutes, and massed a lot of camel archers in no time, subsequently wiping out a huge chunk of our eco. We had quite a hard time trying to stop the Berbers even though our team had a decent score lead over them.

I had no idea what was going on until I checked the record. I really wanted to see how the Berbers player was able to boom so efficiently, only to find out one of his allies was full slinging him from castle age. Then I recalled they picked the same team in the lobby and seemed to be friends.

This is the first time I've seen this in the HD casual games I usually play. What's the general consensus on slinging in a casual game?

Here is the record (HD) if you're curious: http://ift.tt/2AmpykG