The title is disappointing: it implies a causal relationship. The study was an observational study.

Indeed, you can outrun a bad diet: we all know that. The study just shows that the lack of activity isn't the main reason for obesity. Both things can be true simultaneously.

"Running is a statistically ineffective means of weight reduction" doesn't make for a catchy headline. This can suffice.

I agree. A good title could be "You can outrun a bad diet. You just won't".