Which is more stable? CF2 (singlet) or CF2 (triplet)
So generally singlet is less stable as triplet has half-filled orbitals which leads to stability.

However whenever a group that can give  electrons by back donation (examples being lone pair carriers like $\ce{-OH},$ $\ce{-NH2},$ etc. are attached, they stabilise the singlet by back donation of their lone pair into the vacant orbital of the singlet carbene.

This is similar to back bonding in $\ce{BF3}.$