We don't know if the attackers had anything to with the flux of Syrian migrants moving across Europe now, but my guess would be: they had nothing to do with it.
There are about 5 million Muslims in France, which accounts for about 7 percent of France's total population. France has deep, long-standing and often troubled ties to several Muslim nations, notably Algeria. The French presence in Algeria lasted from 1830-1962.
During the Algerian civil war of the 1990s, France was targeted by terrorist attacks several times. One of those bombings EDIT: injured more than 100 people, which may be the number lost in the attacks today.
There are several basic facts that may help people understand why these attacks happen in France (I'm going to make some crude and unsympathetic generalizations that stem from the years I spent there):
* It's close to Middle Eastern and North African countries torn by conflict, notably Libya and Syria. These are training grounds for would-be attackers, many of whom originate in the west.
* Because of that, and of the fact that France rejoined NATO in 2009 and put itself firmly on the side of the US, it is also a proxy for the US, and will be targeted by those unhappy with American policies.
* It's racist. France has not dealt with the fact that people other than the French live on its soil. If you are the child of immigrants who were invited to France to help its post-War growth, you soon learn that a Muslim name will exclude you from many opportunities.
* Its economy is stagnant. France is no country for young men. They will face limited opportunities regardless of their ethnicity, unless they belong to the elite passing through the grandes écoles. This leads to a lot of frustration. When people cannot build a life in one direction, sometimes they are susceptible to morbid, violent ideologies.
* It's sloppy. I lived in France for 14 years, on either side of the 9/11 attacks on Manhattan. The French were really slow to put respectable security systems in place. CDG airport leaked like a sieve for years and I have no reason to believe that has changed.
Anyone who wants to know more about Islam in France should read Gilles Kepel:
https://en.wikipedia.org/wiki/Gilles_Kepel
He wrote a particularly good book in the 1980s called "The suburbs of Islam".
https://en.wikipedia.org/wiki/Sinking_of_the_Rainbow_Warrior