Maybe that was an abberation or to show they had them
I donīt think so luoto 
As others have pointed out, it is just that there is not a standard for giving the infant life jackets. The majority of the airlines will rather do it in case of emergency, but some still prefer to give them systematically together with the ISB.
As for the ISB, in the end I think that it depends on what kind of emergency you are more likely to encounter, because if it is proven that it will save the infant`s life in most cases, in others cases it could be dangerous. So it comes down to what the airline will decide in the end to be the best solution.