Following on from this question, where it's established that druids do not count as 'Shapechangers' for the purposes of effects which relate to them: Are druids "shapechangers" for the purpose of a Polymorph spell saving throw?
If a druid is in beast form using Wild Shape and is affected by the Moonbeam spell, failing his/her save, the following occurs:
When a creature enters the spell's area for the first time on a turn
or starts its turn there, it is engulfed in ghostly flames that cause
searing pain, and it must make a Constitution saving throw. It takes
2d10 radiant damage on a failed save, or half as much damage on a
A shapechanger makes its saving throw with disadvantage. If it fails,
it also instantly reverts to its original form and can't assume a
different form until it leaves the spell's light.
It's not clear to me whether this bolded section means any creature that fails its save reverts to its original form, or only shapechangers revert to their original form.
No, the druid does not revert.
As this is a new paragraph separate from the first paragraph of the spell description, and the paragraph exists to describe the specifics of what happens to a shapechanger, the "it" in the quoted passage can only refer to the shapechanger mentioned in the previous sentence.
Most creatures don't change out of their original form, so it wouldn't make sense to refer specifically to shapechangers in the opening sentence of the paragraph then clarify that all creatures return to their original form.