70-761 Practice exam Question about @@Trancount final value
The expected answer provided in the practice exam is incorrect. Microsoft's own documentation spells out clearly the same thing you've found - every BEGIN TRANSACTION increments @@TRANCOUNT by 1, every COMMIT TRANSACTION decrements it by 1 and ROLLBACK TRANSACTION resets @@TRANCOUNT to 0.

Nested transactions count and increment the @@TRANCOUNT value by 1 as well, so the statement that SQL Server doesn't actually create a nested transaction is also false.

See here for more info. It also does not make a difference if the code is in a stored procedure or not.