From what I've read about the whole deal with this dude (so far anyways) was yes, he was Muslim but wasn't a practicing Muslim ergo not a factor in his decision to do what he did. Also, he had real guns for those who hate them and fake guns for those who want to make the argument against toys looking too realistic.
The media reports as they "discover" the info, typically prematurely, which influences via bias the watcher/reader on how they should feel - continuing to fuel the current debates regarding all these hot-button topics. Add all that together and you seemingly have a bunch of people trying to place blame on a random act of violence when the blame (this time) should be solely placed on the perpetrator and not a group.
I may have outdated or incorrect info about the Nice attack, or even completely wrong, but when I made the meme, and all I've seen thus far from people reacting to it, it was a terrible act of violence and murder by a disturbed individual and not a "formal" terrorist organization.
Could always be a bad and incorrect meme though. Certainly not meant to attack anyone here or dismiss the tragedy in any way. <3