I suspect this is simply an old question; the restriction on title length was put in place in May 2010 and the question is older than this change. The Title column in the Posts table is a nvarchar(250).
There are only 325 questions with titles longer than 150 characters; so, I don't see this as a major problem.
The "proper" solution would be to change all of these questions to have a title length of 150 or less characters and alter the column or add a constraint. I'm not sure it's worth the bother; it depends whether all the checks are done in code, or not.
Interestingly, the newer Stack Exchange sites have a maximum size of nvarchar(250) as well; a just in case thing?