Hi, it does resemble etching or engraving (which I think is the idea) but it definitely isn’t. I’m not sure you could get such a fine detailed image with just acid etching - it is very small.
I wondered about the dots in the mane, as they are not all connected to the rest of the image. Also the rear legs look like a stamped image where there wasn’t enough ink which was confusing.
When people talk about transfers, I automatically think of the sort in Airfix kits where you float the transfer off paper in one go - the image of the horse didn’t seem to fit with that type of transfer (because of the mane and leg issues).
From looking online I believe they screen print the entire image (as Lustrousstone says) in three layers onto a rubber type block. This is then pressed against the glass to transfer the image before being fired on. I think they used that process or very similar for the horse and that would account for the mane dots and the rear legs.
It’s hard to describe how coarse two main layers are, not very, but like a layer of varnish or paint rather than a thin stain. There is a texture of a very fine grid visible in the most translucent layer (hard to photograph) that I assume is left over from the screen from the printing process. I can’t tell if it’s the doubling of two main layers that add to the opacity, or if there is more ‘pigment’ in each layer.
There is some info about the type of process here:
https://books.google.co.uk/books?id=wuD5JHZ7ajIC&pg=PA174&dq=screen+print+transfer+glass&hl=en&sa=X&ved=2ahUKEwiumZTpjr74AhXLOcAKHWmQDQgQ6AF6BAgMEAM#v=onepage&q=screen%20print%20transfer%20glass&f=false