I think that as long as he wasn't just living with them and being a drain on their resources and he was doing something with his life (like working or going to university), there's no problem with that. It's understandable and quite responsible to know his limits :)
It's fine man, you really don't need to explain yourself to people. Use this living arrangement is a means to filter out certain women. As you can see from a few of the female comments below it's a hard idea to grasp for some.
I moved in with my mom for a year when i was 30. The bare minimum amount of time to save enough to buy my house. For the most part women don't want to hear the explanation. All they hear is "I live with my mom..." they've already checked out.
The point is you're young, no kids (i assume), you're gainfully employed, you make decent money. You're doing better than most people.
i think it's cool. i was making $70k a year for a while and lived with my dad for 3 years simply because it didn't make sense to go into early debt over a house and i didn't have the savings out of college for a down payment on a house