My theory on concrete and plants:

1. Thats a LOT of dirt and material without any competition for the roots.
2. Water/moisture is in the cracks/holes/etc.... so it helps the plant with constant moisture control.
3. Some plants know how to take care of rocks and paths are just big rocks.
4. Random selection as this one seed is extremely good at surviving.

Just some thoughts. I have a fruit tree that LOVES it next to concrete. I get fruit every year from that thing.