I don't know that I have ever heard the word used in this way, to describe life. But since buoyant means positive, light, floating maybe it would describe a lighthearted person, someone who sees the good in life and concentrates on that rather than the negative things in life. It could mean happy and carefree, the opposite of unhappy or worried, etc.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.