Almost, but you get exactly the point. It will continue to 'grow' as in flower big fat buds. That's the thing, once transitioned it will stop growing (vegetating) and start flowering. It creates roots like it creates branches and stops doing so around the same time. It will continue to grow roots but just a little, nothing compared to what is has done so far. During veg the plant grows roots and stems and leaves, during flower it uses those to create flowers/buds. So like I said in my first reply, it's not worth it at this stage.
And again, even if you had a larger pot to begin with, the roots will continue to grow down till they reach the bottom. Comes with growing in pots, it's not something you can avoid entirely. Doesn't meant the plant is root bound though.