ISIS has claimed responsibility for the attack, but experts are doubtful (and ISIS has made false claims before–big surprise–murderers also lie) so I’m skeptical of this claim until we learn more. I’ve seen that it’s very possibly a false claim from multiple reliable sources.
These sites are not good sources for news. They are looking to get a ton of shares by playing to your bias or stoking your outrage with sensationalist headlines. Usually they don’t even contain original content but just repeat what other actual news sources are saying but dialed up to 11 on the outrage scale.
I would add to the list in the link above a website called Washington Journal, which I’ve seen shared a lot. I don’t consider it a quality news source. It’s sensationalized and designed to garner outrage on the left. I can’t precisely speak to how factual it is but I wouldn’t trust it until verified from a more reliable source. I will probably call it out when I see it. (Not to be confused with the C-SPAN show, Washington Journal, which is a whole different thing.)
Here are some helpful links to check before you share a link on social media. If more people were careful before sharing, there would be fewer false stories spreading and fewer crappy so-called news sites gaining clicks. It will avoid you getting an annoying comment by someone like me who likes to fact check.