Shane Caulde, the creator of Tappy Chicken, posted the following about the game over in another post. Link to Original Post
<< “Hi, Tappy Chicken does not use lighting. I just made the material unlit. You can change this in the material, set the lighting mode to Unlit, and run your diffuse into the emissive channel. The Chicken animation is done by offsetting the UV’s in the material. If you open the chicken material you can see how this works. You basically just tell the material how many rows there are in the texture, and then just feed it what frame number you want. I do this with a timeline. You can find it on the lower left of the Blueprint. Also, if you doing an unlit game, go to Edit/Project Setting/ Rendering and uncheck Mobile HDR. This will turn off lighting all together, and will give better performance on low end devices.” >>
In regards to this, there are the textures (sprite sheets) that are imported and then a material (that UE4 uses and can be applied to any planes or meshes) is created based off that texture. The material that is created is using UV offsets for the animation of the chicken. However, if you look at the meshes for any of the other objects (ie. menu buttons or the obstacle poles) you can see their UVs are setup to be unique and to use a specific space on the material/texture.
If you have any other questions feel free to ask!