I believe the question here masks an even more serious problem.
"Why was a sample-paper not provided in the first place?"
I 100% agree with the student's assessment that the format of an exam is absolutely critical knowledge which largely dictates the type of preparation for that exam.
I 100% disagree with the (in my opinion naive) comments above that "if you really knew the material it would not matter". One need not think further than driving tests as a simple example that this is simply not true.
The question of whether an exam "should" be generalizable enough such that it accurately reflects the topic it is supposed to examine, and how to achieve such an exam, is an altogether different question which has plagued educators for centuries. But as it stands, one can guarantee a crippled outcome in an exam if exam technique is unaccounted for, let alone misdirected.
So yes, the act of 'not providing a sample paper in the first place', let alone misrepresenting the format of the exam when described orally, (whether this was done maliciously, which is very unlikely, or by omission), is absolutely fair grounds for a complain to the department, because the department is responsible for ensuring exams are fair and representative of student's abilities.
Note this is not a case of 'burning' the professor involved. The department absolutely needs to know so that it can manage the delivery of its courses better. And if there are no departmental guidelines ensuring appropriate provision of sample-papers to students, this will hopefully prompt them to create such a guideline.
PS. Many of the answers here have given far too much weight on the word 'unethical' in the title, and have interpreted this and focused instead on whether it is appropriate for the student to be 'throwing accusations of intent'. While this is a reasonable, albeit secondary, point to address, I believe this is missing the point entirely, and it doesn't sound to me like, bar some frustration for the feeling of unfairness involved, that the student is somehow on a personal crusade against a professor. It is entirely accurate to state that the format of the exam is necessary information, and it is entirely fair to initiate a grievance procedure if this has been misrepresented to the extent that it affected student outcomes.