if the moon was a disc then looking at it from any angle besides head-on would result in it looking oval shaped
It depends on how far away it is and how far you move in relation to that distance. If the moon is very far away (as is believed) and your motion on the earth is relatively very small - then it is very unlikely you will be able to detect any such minuscule shape deformation (especially with your eyes). In much the same way as the sun changes size as it increases and decreases distance from us - it is very difficult to detect for the same reason(s).
But there's only one shape that appears as a perfect circle no matter what angle it's viewed from, and that's a sphere.
Of course not, but if your vantage to it is limited - it certainly can, and can even be perceived to be convex when it is not. That was my only, admittedly minor, point.
It depends on how far away it is and how far you move in relation to that distance. If the moon is very far away (as is believed) and your motion on the earth is relatively very small - then it is very unlikely you will be able to detect any such minuscule shape deformation (especially with your eyes). In much the same way as the sun changes size as it increases and decreases distance from us - it is very difficult to detect for the same reason(s).
It could be concave as well.
Concave wouldn't look like a perfect circle from every angle
Of course not, but if your vantage to it is limited - it certainly can, and can even be perceived to be convex when it is not. That was my only, admittedly minor, point.