This history is pretty seriously flawed in almost every paragraph. While ARPA was funding an internet for the military and related educational institutions, corporations were funding internets too. The breakthrough to "Internet" (Capital "I) was about 1988 when you could go to a terminal and type in a path through various internets to any other person/machine.
There were individual people such as Bob Kahn (see https://en.wikipedia.org/wiki/Bob_Kahn where you can get better info...he was originally "BBN" and then was at "ARPA" funding it. Vent Cerf was the other guy :-).
For you Python nuts on medium.com, Bob's DARPA funded efforts created Python at CNRI where he is still the CEO.
What DARPA did was to define and most importantly fund the protocols that stuck the Internet together. They also funded the Mach Operating System which is also the operating system underlying Windows NT and the MAC...and by the way your phone. All speaking these Internet protocols.
My wife, in 1976, was one of the two people at Bell Labs writing "shell scripts" for "Programmer's Workbench UNIX" which allowed ATT employees to log into a machine and do work which they thought was a mainframe (e.g., IBM, Boroughs, etc.) but was actually a DEC PDP-11 networked somewhere in some place in the "vast" AT&T Telephone system. I quoted "vast" because it was certainly only "vast" for the time. UNIX (and portable C) were simply faking being mainframes with shell scripts and C code, and faking their locations too. Lower case internet was mature by then for corporations.