In an earlier life I was a sign interpreter for the deaf. Actually did court room interpreting in San Diego. About 95% of the time it included hand signing. But, one man grew up hearing and became deaf later in life. Sign language was very difficult for him and he relied on lip reading. So, when he went to court I did NOT use sign language but mouthed the words. It's often difficult to understand lip reading from unfamiliar people (mustaches, fat lips, etc).
Not at all unusual for a marginally signing deaf person to rely on an interpreter that he / she can easily lip read.