But is it only the legend?
When I visited the HK's island Lantau one day I went to swim in sea. I have been on a rocky beach. The rocks were carved by water but on some rocks you could perceive something like animals footprints. On one of the rocks I noticed a footprint looked like the footprint of a giant bird. I took a photo of it and I am presenting it on the photo on the left side. On the photo on the right side for comparison I am presenting footprints of contemporary birds. Gerrie McCall in his book "Dinosaurs"described some of these animals as digitigrade, it means animals whose stand or walk on their digits or toes like birds or cats. So the footprint on the left photo could be left by a dinosaur.
OK, but what about people?
If the rocks with footprints are in similar age it could point on that, that people and dinosaurs walked on HK's swamps in ancient time and met each other. So the name Kowloon - nine dragons could mean real nine dragons - dinosaurs which lived there long time ago.
It could be also that the traces what I showed on the photos above were made by water.