This question is almost more about TRUNCATE than IDENTITY. All of the inserts before the TRUNCATE are just red herrings.
To some extent I agree, but I would say that you have to know what inserting a row in a brand new table does to its identity column as well as knowing that TRUNCATE puts the table into the brand new state.
Of course I haven't a clue why the author thought that the remark in the explanation about a table not having multiple identity columns had any connection with the question or the answer .:rolleyes:
Apart from the explanation it's quite a nice question. 😎