THC lingers in breastmilk with no clear peak point: When breastfeeding mothers used cannabis, its psychoactive component THC showed up in the milk produced. Unlike alcohol, when THC was detected in milk there was no consistent time when its concentration peaked and started to decline.

I don't think this study invalidates the anecdote whatsoever. Long term caloric deficit has different effects on the body than a 24 hour fast does; chronic users have entirely different anatomical contexts than people who have abstained for an entire year; and so on.

If you wanted to really invalidate this anecdote, you'd need a long term experiment with chronic smokers as your subjects who would need to gain weight while being a chronic smoker, abstain for long enough for cannabinoids to be undetectable, and then lose weight rapidly while continuing to abstain.