There are some zen quotes and teachings that compare our minds to the contents of a cup vs the vessel (body). In Daoism you have the yin/yang aspects. Afaik The quote seems to be his.
That quote is indeed his. I listened to Shannon Lee's (his daughter) podcast, and she told the story of when he understood it.
Apparently when his martial arts teacher told him he was too forceful, to be more like water, and then banned him from practicing until he understood. Short story, he went on a boat ride, got angry, started punching the river, then he got that aha moment.
Bruce Lee was actually a really wise dude. I also highly recommend the podcast.