$ pkg-config --help
--atleast-version=VERSION return 0 if the module is at least version VERSION
--exact-version=VERSION return 0 if the module is at exactly version VERSION
--max-version=VERSION return 0 if the module is at no newer than version VERSION
While the source code states that it causes the version requirement in read packages to be replaced with the given one instead:
ver->comparison = EQUAL;
ver->version = g_strdup (required_exact_version);
Although the return value usually will be a side-effect of this change, the description suggests that it implies behavior like '--exists'.
Fixed in commit 548ba5b. Thanks for the report.