Consider how our foliage covered Dov friend here had just seemingly registered, me thinks there's a little collaborative thing going on. Either way, this will hopefully prove to be most entertaining.
Not one of the aforementioned "us," but the Elk did ask for people to play along. Always a good time.
If Ysgramor was indeed a "dragon", most likely he was a Dragon Priest - in the Late Merethic Era, it would be unlikely for a leader of Ysgramor's reported stature to be unconnected to the Dragon Cult.
This theory seems to be supported by archaeological evidence, namely Ysgramor's shield and tombs contemporary to the period.
At the time, anyone of high stature or great prowess in battle would have been considered a "dragon" (the highest compliment imaginable). This does not mean that Ysgramor was in fact an actual dragon, but I have no doubt that the literal-minded among us will not hesitate to jump to the most obvious conclusions. True scholars will of course be more circumspect.
Mayhaps you care to present textual evidence? The Nordic visions of a Draconic Talos are an obvious modern equivalent, and so far as I can tell clearly refer not to title or metaphor but to the Nords seeing an actual, honest to Gods Dragon when looking upon Tiber Septim. The occasional eye-witness account of the Graybeards as dragons have in recent weeks also proven to be true. I know of no others to be called dragons in so serious a manner. I think we can all agree on the existence of a Dragon Cult in old Atmora, and therefore the existence of Dragons. We know also that Ysgramor was a great chief among his peoples, and is regarded as a culture bringer by both scholars and theologians. Sounds like a Dragon - or even
the Dragon, see Akatosh in the Imperial heartland - rather than merely a priest.