I suspect there are many more reasons to travel on a stolen passport than terrorism. Especially if your destination is in Europe: What do the immigration people do with those that arrive on stolen passports? Can they return them? Where to? If the "refugees" don't cooperate, immigration will never know where they're from, thus can't ship them back. Apply for asylum and hope you can establish a foothold. That's how economic migration to Europe works these days as far as I know anyway, happy to stand corrected.
The fact that they were travelling to the same destination (if that's true) and that they bought sequential tickets on CSN, all that proves is that those two probably had something to do with each other. Perhaps they were both from the same family. It would be interesting to see some stats on how many illegals arrive at AMS every day.