It seems to me that it’s a chessed. And a big one!
In terms of your uncertainty based on the fact that it wasn’t really needed and he could have hired someone, I would have to ask you, “if that is the case, then why did he ask you to do it?” He must have had a reason. Generally, if someone asks someone to do something, there is a reason. Maybe he likes your work the best and that’s why he asked you.
In any case, it seems to me that just about any time that someone asks you to do something for them and you say yes, it is a Mitzvah as long as it’s not at someone else’s expense.