Mapping a hiking path that is completely invisible on aerial images without having been there just from a description somewhere online is a no-go, I think we can all agree on that.
If all you want is guidance in an app you can follow when you already know where you want to go, just create/import a gps track.
Not sure who claimed that, but you didn’t know either at the time you mapped the path. That’s part of the issue here.
Whether the cairns are sufficient to map a path there is hard to tell from photos alone. Single snapshots don’t really give enough information and cannot replicate the context one would have while physically being there.
Someone in one of the related topics put it quite well in a way that matches my expectations/requirements for a trail in OSM:
I don’t think this requirement is fulfilled here (if we leave out potential physical markings for a moment). One person following a description someone else posted online is not exactly shared common knowledge.
Physical markings on some parts of the path may be enough to justify mapping those parts, but it sounds like they were quite limited.