See as someone into biology/zoology, the external ears and doglike noses were much more "un-reptilian" than laying eggs or having scales was reptilian. There are mammals that lay eggs, and many reptiles that don't, and mammals with scale-like structures, but there are no reptiles with that sort of external ear (or anything even close AFAIK), and no reptiles with mammal-style noses. Nor have there ever been, that we're aware of. At best kobolds were some 50/50 mixture of characteristics.
The monotremes lay eggs but that is only the platypus and the echidnas. None of them are scaled. A very small subset of mammals.
There is the pangolin, which has fingernail type scales, but that is also a tiny subset of mammals and they do not lay eggs or have horns.
No dog has scales or lays eggs.
The vast majority of reptiles both have scales and lay eggs. There are viviparous reptiles who give live birth (boas, water snakes, about half of skinks, and the viviparous lizard among others) but egg laying is very common.
When I saw the B/X and AD&D 1e pictures and descriptions of kobolds horned lizard people comes to mind easily, adding on a few dog features. I can see someone thinking pangolin people could work too if you add on dog noses and egg laying and horns. Or dog people at base adding on horns and scales and eggs to that base.
I would say their first art and descriptions are definitely a mix of disparate dog and reptile aspects and I feel it is an effective mix for a D&D monster people.
I did not care for the pug dog people original 2e art for kobolds at all in the Monstrous Compendium I.
The later 2e Monstrous Manual art was OK, though it adds hair and I can't really make out any scales and seems more rat person than dog person.
The 3e kobold seems to take the di'Terlizzi thin spindly one and make them more explicitly reptilian and changes the color from rust to more green (which I always pictured the 1e MM black and white kobold images as being despite the description as rust color).