Both run on unshielded twisted pair, i.e. two copper wires twisted together along the length of the cable. The effect of this is to generate less electromagnetic radiation and crosstalk, avoid interference with other wires or components, and resist interference from other sources.
However, 100Base-TX uses two twisted pairs, while Automotive Ethernet only uses one pair, so it is less weight and cost. This set of pairs is “balanced”, i.e. the signals have equal but opposite voltages. Both transmit and receive signals are conducted on one set of twisted pairs, rather than two separate sets of twisted pairs like 100Base-TX.