Insert fails within transaction, but sql server returns 1 row(s) affected?

Question

This is the execution flow of my stored procedure:

ALTER procedure dbo.usp_DoSomething

as

declare @Var1 int
declare @Var2 int
declare @Var3 int

select 
@Var1 = Var1,
@Var2 = Var2,
@Var3 = Var3
from Table
where  
...

BEGIN TRY
    BEGIN TRANSACTION
        /* UPDATE Table. This executes successfully */

        /* INSERT Table. This fails due to PK violation */

        COMMIT TRAN /* This does not happen */
END TRY
BEGIN CATCH
    IF @@TRANCOUNT > 0
        ROLLBACK TRAN /* This occurs because TRANS failed */
END CATCH

The UPDATE runs successfully. The INSERT fails, so the transaction is rolled back.

After execution, the table looks correct and nothing has changed. But when I run the SP, I get the following messages:

(1 row(s) affected)

(0 row(s) affected)

So I'm asking myself, where is the first 1 row(s) affected coming from?

Then I'm thinking that this is the reason, but wanted to confirm: OUTPUT Clause (Transact-SQL)

An UPDATE, INSERT, or DELETE statement that has an OUTPUT clause will return
rows to the client even if the statement encounters errors and is rolled back.
The result should not be used if any error occurs when you run the statement.

Answer 1

By default, a rowcount will be returned for every DML statement, unless SET NOCOUNT ON is enabled. Regardless whether a transaction is successful or not, or rolled back or committed, your UPDATE statement was successful, thus the notification (1 row(s) affected).

The OUTPUT clause you mentioned has nothing to do with it, since you haven't specified it.