Without a job for six months due to taking care of his ailing mother is easy to explain before the employer.
First, he must be honest why he resigned to his managerial job so that the employer knows the reason of his exit in his previous job. With this, he can established dignity with great pride that he left the company with a clean record.
Second, he could also tell that he wants to enhance his skill and look for better opportunities in other company.
Lastly, he can also explain that while taking care of his mother, he at the same time had enrolled for some advanced personality development course to improve himself further.