The timeline is off. The antitrust complaint was about xerography, which did not come out of PARC.
There IS a connection, though: Xerox settled the suit by licensing its patents, which led management to think "holy shit, we're losing the monopoly, we'd better do something" and start up PARC.
You are right, I was thinking about this earlier and that I think the government forced Xerox to release laser printer patents in the mid 1980's but as an unpaid internet commenter I ended up at an article from a decade before then.
“Following these years of record profits, in 1975, Xerox resolved an anti-trust suit with the United States Federal Trade Commission (FTC), which at the time was under the direction of Frederic M. Scherer. The Xerox consent decree resulted in the forced licensing of the company's entire patent portfolio, mainly to Japanese competitors. Within four years of the consent decree, Xerox's share of the U.S. copier market dropped from nearly 100% to less than 14%.[31]”
There IS a connection, though: Xerox settled the suit by licensing its patents, which led management to think "holy shit, we're losing the monopoly, we'd better do something" and start up PARC.