that I cannot confirm as I cannot access your lab environment, but how much you shared my test cell is same.
Yes correct the arguments use by is perfectly correct but remember the test cell of hazard ratio is also using one_hot_train function which is from the previous grade cell.
So things to check would be did you use dataframe arguments to the get.dummies( ) to get one_hot_df. If yes, next check point is in hazard ratio, make sure your code is not hard coded.
The target.name is transpose tuple value of case 1 and case 2 which inturn is tuple value of the cox_params.dot to which numpy.exp need to be used to calculates the exponential of all elements in the input array.
Regards
DP