Companion plants

Last fall, I dug three geraniums out of their outside pots and brought them inside. They have been enjoying the sunshine in my office window, and so have some strangers. In one pot has sprouted pale green, bean-like leaves that I'm guessing is a sweet potato vine (above). I dug it out and gave it its own space, and it is taking off like crazy.
In another pot, I suddenly noticed a tomato seedling almost as big as the geranium it is happily sharing space with. This will not end well. I can't imagine what would happen if I continue to let them cohabit.
So how did these strangers become companions? One geranium came from an outdoor arrangement that contained some sweet potato vines, and I suppose a piece lay dormant for months and suddenly decided to spring to life. But the tomato is a mystery.
It is endlessly fascinating that plants will spring from wherever they can find a foot hold. But it also gives me hope that no matter what we do to this planet, life will persist.