Contains minor spoilers about the show Vikings

Hey, having seen the latest episode of the TV show Vikings I was wondering if it's accurate that the Normans used crossbows already. I did some research on Rollo the Viking who became the leader of the Normans at around the year 900 but it's hard to find accurate information about crossbows. I read that, in europe they started commonly using them in the 13th century. Now, the Normans have been using a lot of crossbows in this episode, the usual simple medieval type. Does that make any sense for that time (late 9th century/early 10th century)? Also, I found it a little weird that the Vikings were using crossbows too (sure they could have gotten them from their pillages) but also in a very treacherous way where the enemy had no chance to fight back, I don't think they even had weapons. As far as I know the mentality of the Vikings was all about honour and fairness. So, am I wrong here or would that have been very unlikely?

Thank you!