I am also not very aware of what they did and also I am fairly new to this. But here is an idea of what they did. They extracted 1d feature as suggested on the top part of the image and also extracted the 2d features from the data (feature generation can be done in many way so not a problem). But the intriguing part for me is how these 1d and 2d features can be combined to train one single network (here in this case 2D resnetv2 ) as presented in this picture.
Sincerely
Raj