Does it sound natural?

1. Oliver lived (or was living in Paris) when his friend got married.

Note: To me, "was living" sounds more natural. The reason is that "living" is a continuous action.

2. I saw the thief just as he ran away (or was running away).

Note: To me, "was running away" sounds more natural. Same reason as above -- running away is a continuous action.

But -- both are correct. No matter which one you used, no one would give you a funny look.