Originally Posted by Virgocat
If you say "Their spirits were buoyed.", it means "Their spirits were lifted."
spirits - represents mood, feelings, morale - in this case
If one's spirits are lifted - or buoyed - then one feels better. We could also say that one feels more encouragement.
To really understand this, I think it's important to take a look at the definition of "buoy". It can mean a couple different things. It's a noun and a verb.