I agree with your rant, this kind of title is annoying.

I do however also think that doing slow mindful walks will help against stress, so the implication that slow walking brings happiness is not a bad implication. Stressed out fast walking people really should try it. There's no reason to be in a hurry all of the time.

But the headline doesn't imply a causal connection, it's your own bias that does

I read it and immediately assumed it's because stressed people walk faster

I didn't even think about taking the title seriously but now that you say it, it does sound ridiculous. I wonder if it's bait for people to come in explain causation (serious) to drum up engagement, or if it's actually just dumb.

Headlines to drive clicks, that's all it is.