Grand Theft Auto IV weird experience

One day of december of 2012, I was playing with my PS3 the game GTA IV. It was on friday evening at about 6:00 p.m., like a normal day. When i went out of the other boring lobby and entered another one, i noticed it had some strange users. They were 5 users, without me included. I had my bluetooth headset on and i could hear at least 2 of them speaking very strangely, i didn't understand what were they saying because their voices were very distorted. We were all inside the airport because that is the most popular place in the map. I appeared at the parking lot but i didn't see any parked cars or pedestrians. I walked to the runway and saw the classic mods. Dinosaur skeletons, flying cars with neon lights, skateboard ramps, helicopters without propellers, and other vehicles that were not available online. The strange part about this was that i had never seen all those vehicles in the same lobby, only separated. I took my camera to be prepared for any other weird thing. Then i took a bike and 30 seconds later i got on fire and died. Other 3 players died too in the same way, but 2 of them were riding a dinosaur skeleton and the other one was walking. This makes me think that the other 2 players were the ones who put mods. They were in the jumbo plane in the sky, speaking to each other. One of the players tried to kill them by taking a hellicopter and starting to shoot missiles at the plane. This didn't work obviously, the plane was intact and the helicopter suddenly exploted and the player died again. Then all the screen got blue and our characters started to fall as if they were in the sky. I only saw mi character and the other 3 falling. The 2 hackers were not in the map but i could hear them laughing very creepily, I tried to go out of the strange lobby but then the videogame freezed and i had to turn off the PS3. unfortunately i forgot their usernames because i was very entertained taking photos to the game. But i do still remember that both were with numbers, capital and small letters (like Qw3RtYy). Here are some photos i took while playing there: