The interest rate of your loans has no effect on your credit. You will pay off the loans quicker if you concentrate on the high-interest rate loans and as a result your credit utilization ratio will go down which will improve your credit, but you could achieve a lower credit utilization by paying off the loans with the lower interest rate as well so your statement is misleading.
While repaying your debt more slowly or at a lower interest rate is better than not paying it at all, a debt management plan can still adversely impact credit scores. Although enrollment in a debt management plan isn't a factor in credit scoring models, it can affect other aspects of your credit that are common factors in many credit scoring models.
A debt management plan sets up a payment schedule for you to repay your debts, with the goal of helping creditors receive the money owed to them and ultimately improving your financial and credit standing. By voluntary agreement, you deposit funds with your credit counseling agency each month, who sends those funds directly to your creditors. It usually takes 3-5 years to complete payments under a debt management program, after which you may be able to reestablish credit.