Yes, it does mean they're not a group. It means they're at best a collection of many aligned groups. It's literally not an organisation, because it's not organised. It'd be just as incorrect as calling the French resistance an organisation. To be an organisation requires that it be organised. It's not. There is no person in charge of it all, there is no membership. In what sense is it an "organisation"?
No, but they were a hell of a lot more organised than antifa, and therefore closer to an organisation. They had distinct leadership, recruiting and membership, there was a hierarchical structure. The people in individual cells might not know any others, but the people above them did, and you could draw up an organisational chart for them showing the entirety down to the individuals if you had the knowledge. No matter how perfect your knowledge, you couldn't draw up such a chart for antifa, or right out their rule book. One "cell" of antifa might be a bunch of mates from school who decide to start attending protests one day, and calling themselves antifa. There's no one who'll tell them not to, no spokesman who goes on tv and takes credit for actions in antifa's name, or disavows ones they don't like.
It's as meaningless as saying Star Trek fans are an organisation, or over 60s are. There are groups of them, some of those groups get together with others, or even organise large meet ups. Some of those groups will have leaders of sorts. They're still not an organisation.