While unveiling iPhone X, Apple made a statement to this end:
With Touch ID, it stated that there was a 1 in 50,000 chance that someone would be able to open your phone with their fingerprint. These numbers were a little better for Face ID, at 1 in 1,000,000.
This seems strange as fingerprints are known to be quite unique, though I'm not sure how unique one's face is.
In this answer, a graph puts face lower in security to fingerprint:
Are these claims (by Apple) realistic and what is the possible maths behind them?