I'm a conspiracy theorist and my take on it is: it looks to me that the cat has allowed the kid to use it's bike. It's the cats bike.
The dog next door obviously hasn't got a bike and is and has been jealous of the cat having one. Obviously there's been trouble with these two before over the cat getting everything whilst the dogs owners get him nothing and I think they have both had a few fights, with the cat winning.
What seems to have happened from this point is pre-meditated.
The dog has hatched a plot to steal the cats bike and ride off on it. It's seen the kid on it and not realised the cat was maybe sat reading the paper in a deck chair or something.
The dog took it's chance and dragged the kid off, ready to steal the bike. The kid's screamed and the cat's flung it's paper down and ran at the dog in a rage.
If you look carefully at the dog running away on the right hand side of the car, you can see the cat mouthing, " you won't be doing that again, pal, 3 strikes remember and this is your third."
If you look closer, you can see the cat run its paw over it's throat as it says those words.
The dog was stupid because jealousy has obviously cost him his liberty and death row. The cat will no doubt get a medal for his actions and maybe a nice fish.