Literally take a dog for a walk up a mountain, it gets tired, "oh wait it must be someone who left a big bag of weed and my dog gobbled it up when I wasn't looking".

Not in this case. Dogs have more cannabinoid receptors than humans so THC can easily put them in a coma.

Actually wait, this article is complete bullshit.

Bluhme said Tokyo had made a full recovery after the incident during a trip to Scotland last weekend. She said vets believe she ingested cannabis left on the trail.

The vets made a guess, their best guess based on very limited information.

TIL Apparently dogs can get a severe reaction to THC from eating poop of someone who had digested cannabis.

Okay that's a few steps beyond "discarded".