This was a fascinating event in the space law scene when it happened. Basically, they didn’t get a launch licence from the US government, and ISRO never asked for it and so just launched it up there.
Since Swarm is a US entity, the USA is legally liable for any damage that Swarm’s satellites cause in space, as a result of the Outer Space Treaty. But while local laws from ratifying the treaty generally said/say it’s illegal to launch as a citizen without a licence and some level of insurance, in the US there wasn’t really any mention of what the punishment was supposed to be - it was written at a time when it wasn’t really expected that a citizen could soon launch a satellite without a licence! 😂