Once upon a time, the different extensions do mean different things.
Like a dot com is the general extension. The dot net is supposed to be a network. The dot org is supposed to be for organizations. Today, it has become a free-for-all. The dot com is the goto extension. So when you cannot find a dot com for the name you want, you go to the next available extension, like a dot net or a dot org.
I think there are only a few extensions with very strict vetting. Like dot edu. You have to be an accredited education body to use the dot edu. Of course, to use dot gov, you must be a government department. Other than that, you are free to register your domain with any extension you wish.
Even with country specific extensions. Like, if you are not a US resident, but you want to acccess the US market, you can still find a company which will make it possible for you to register a dot us domain name.