Curl definitely should be updating man pages if it is falling back to OpenSSL CAs when --cacert is specified.
Homebrew Curl on Mac also sets this flag:
https://github.com/Homebrew/homebrew-core/blob/9cccce7a6dff7...
And at least according to curl's code is set by default when it is built against OpenSSL:
https://github.com/curl/curl/blob/1ccf1cd9936dfa382fe1f061b6...