Well, of course it it a song about the 1st world war. But to deduce from the message of peace a link to the terror in Paris is quite vague. (By the way, it was written before the attacks, so a deliberate intention to commemorate them is excluded). You could interpret ANY conflict around the world out of a peace song. And that's what makes the difference to the armenian song. It's a general topic, not a specific one. Furthermore, in the 1st world war, there have been victims in all european countries, which makes the topic even more a common one. No one will thus object it or be offended. As for the armenian genocide - its about the victims in one people and you know that the topic is highly controversial (a discussion I don't want to start here!). So bringing up that topic in the esc would create tensions which the EBU wants to avoid.
Don't get me wrong - I personally find the song great and touching and I have the greatest respect for the artist and his goals. I just said - I think EBU would not let this enter.