Mark you exaggerate! The 'neighbour' lives about 50 km (30 miles) away...
I've somehow never opened this post. I recognised the flower as something from my parents' Johannesburg garden. It arrived (literally) on a rock I acquired from another garden, survived and grew. 10 years on it is impressive, tends to be invasive, but is easy to control. (It HAS moved off the rock
)I.e. I don't think it roots from remnents, because then it would be much less contained. I remember finding out what it was and being surprised, so the lobelia tag fits. In fact I've been wanting (a) to re-identify it for some time and (b) get some for my own garden. So thanks!
By the way - they have no frost there, so if anything it will spread more slowly for you. A part has grown over two meters into a Japanese sacred bamboo (Nandina domestica) where it looks lovely and has been left 'to do its thing.'
By the way, your setting looks lovely - more pics please! And welcome to both you and -oops- I'm editing so I can't check: the Oregon USA gardener with the lovely dark red flower (hollyhock?) avatar.