You can express a circuit as a graph, and many schematic formats are plaintext. Same goes for the Gerbers which are an ASCII format used to describe the masks that are used to define the PCB traces. The models are trained on a lot of academic information about how circuits work, most component datasheets are public and they've sucked up all sorts of niche greybeard advice from internet forums.
A huge advantage of electrical design is that the connectivity is testable with Design and Electrical Rule Checks (DRC/ERC). I suspect you could even tell the models to run physics checks on the traces that are important for things like crosstalk.
A huge advantage of electrical design is that the connectivity is testable with Design and Electrical Rule Checks (DRC/ERC). I suspect you could even tell the models to run physics checks on the traces that are important for things like crosstalk.