Why does SQL Injection not happen on this query inside a stored procedure?

I made the following stored procedure: ALTER PROCEDURE usp_actorBirthdays (@nameString nvarchar(100), @actorgender nvarchar(100)) AS SELECT ActorDOB, ActorName FROM tblActor WHERE ActorName LIKE '%' + @nameString + '%' AND ActorGender = @actorgender Now, I tried doing something like this. Maybe I am doing this wrong, but I want to be sure that such a procedure can prevent any SQL Injection: EXEC usp_actorBirthdays 'Tom', 'Male; DROP TABLE tblActor' The image below shows the SQL above being executed in SSMS and results being displayed correctly instead of an error: Btw, I added that part following the semicolon after the query was done executing. Then I executed it again, but when I checked to see if the table tblActor exists or not, it was still there. Am I doing something wrong? Or is this really injection-proof? I guess what I am trying to ask here also is that is a stored procedure like this safe? Thank you.