The internet is a grid of computers to which you connect.

More than that though, conceptually "off-the-grid" means not accepting a utility serivce from a provider but rather catering for that yourself. An internet connection is arguably a utility, and you'd be accepting it from an ISP. That goes against the concept, which would suggest you should maintain your own isolated network of computers and not connect with the outside world.

You wouldn't have to be isolated. You could make connections, just not ones that depend on a centralized ISP.

But "off-the-grid" typically is talking about physical delivery over wires and pipes, not about things like wireless internet.