This is with regard to SC 3.3.1 Understanding doc at https://www.w3.org/WAI/WCAG22/Understanding/error-identification.html
Reference the following pieces of text:

1. "Whether or not an error message provides users with sufficient information about the nature of the error, and what they should do to correct it, is covered more specifically by 3.3.3 Error Suggestion".
   Comment: The text message for the error as per SC 3.3.1 must really "provide users with sufficient information about the nature of the error" to understand what is wrong with the input data provided. This is not a requirement of SC 3.3.3. So this guidance is incorrect IMO.
   SC 3.3.3 only deals with how the error can be corrected.
   It will not be out of place to add- sometimes the wording of the input error description can be so that it meets both SC 3.3.1 and SC 3.3.3 simultaneously.
   For instance, "Please provide a valid email address" as the error description conveys that email field is empty or invalid and also how it can be fixed.

2. "An "input error" is information provided by the user that is not accepted. This includes:..."
   Comment: Better / semantically accurate wording could be:
   "An "input error" is input data that has failed validation for the application preventing access to further processing. This includes:..."
   The "failed validation for the application" also helps to explain the phrase in the SC "automatically detected".
   Thanks,
   Sailesh