Etymonline's comments simply say:
terminal (n.) "end point of a railway line," 1888, from terminal (adj.); sense of "device for communicating with a computer" is first recorded 1954.
Wikipedia notes that there is an electronics term for "terminal":
A terminal is the point at which a conductor from an electrical component, device or network comes to an end and provides a point of connection to external circuits. A terminal may simply be the end of a wire or it may be fitted with a connector or fastener. In network analysis, terminal means a point at which connections can be made to a network in theory and does not necessarily refer to any real physical object. In this context, especially in older documents, it is sometimes called a "pole".
Thus, with regards to networking, the use of "terminal" in railway connections were probably applied to computer networks. The "terminal" would be the connection to the network.
Furthermore, Wikipedia's entry on telecommunication terminals describe them as such:
In the context of telecommunications, a terminal is a device which ends a telecommunications link and is the point at which a signal enters and/or leaves a network.
More evidence for this connection is under Etymonline's entry for "network":
network (n.) "net-like arrangement of threads, wires, etc.," 1550s, from net (n.) + work (n.). Extended sense of "any complex, interlocking system" is from 1839 (originally in reference to transport by rivers, canals, and railways). Meaning "broadcasting system of multiple transmitters" is from 1914; sense of "interconnected group of people" is from 1947.
The term "terminal" was introduced not long after the term "network": 1888 and 1839 respectively.