To be that far out is an acomplishment to be sure but its got a very long way to go before it actually leaves the solar system.
To technically leave the solar system it will need to be outside the sun’s influence beyond the most distance orbiting objects. It shouldn’t take but another 26,000 years or so. Its still inside the closest orbit of Sedna.
They believe Sedna may be a member of the Oort Cloud, and the Oort cloud extends over two light years from the sun. If two light years from the sun isn’t interstellar space, then there is no such thing as interstellar space. I doubt you will find many who believe two light years from the sun isn’t interstellar space, and that our Solar System extends over two light years.