By default, Redirect sort of maps the path node to a new path node, so anything after the first path gets appended to the target URL.
Try:
RedirectMatch 301 ^/abc/cba/ http://www.aaa.com/?
Or if you’d rather use mod_rewrite instead of mod_alias:
RewriteEngine On
RewriteRule ^/?abc/cba/ http://www.aaa.com/? [R=301,L]