Clarify regex interpretation in str.contains

Fix GH44811

Author: nealmcb

pandas/core/strings/accessor.py

@@ -1212,8 +1212,8 @@ def contains(self, pat, case=True, flags=0, na=None, regex=True):
         """
         if regex and re.compile(pat).groups:
             warnings.warn(
-                "This pattern has match groups. To actually get the "
-                "groups, use str.extract.",
+                "This pattern is interpreted as a regular expression, and has match groups. "
+                "To actually get the groups, use str.extract.",
                 UserWarning,
                 stacklevel=find_stack_level(),
             )