Almost any of the explanations are feasible. I'd like to throw in the fact that Ancient Celts spanned a very wide area in Europe...as far East as Northern Turkey and well down into the Iberian Peninsula. Some bit of documentary that I recently saw parts of on Youtube pointed out similarities between some forms of Irish music and dance and those of Northern African cultures. The reasoning seems to be that there was a flow of culture through the Iberian Peninsula and by sea along the Western coast of Europe up into the British Isles. Surely the image of the lion was very well known in Northern Africa and in the "nearly Middle Eastern" part of Ancient Turkey.

Just another possibility to muddy the waters!

Best

AA