The episode begins with a flashback of 17 years to an 18 year old Matt. A "couple of years" before the war might be 1859 or 1860, so "present time" for the episode might be 1876 or 1877.
As to the telegram, it might have been a ruse to trick York, as word of its contents filtered back to York. At the end, Matt had his badge in his pocket and pinned it back on.
The viewer did not get to learn of Matt's plan, unless Matt foresaw that York would behave the same way twice.
In the flashback, all the people with York seemed like Southerners. York claimed to have a pardon from General Grant. Not clear how that could be. President Grant could not "pardon" criminals for state law crimes, such as homicides. As to pardoning Confederate enlisted men, President Johnson did that December 25, 1868. Grant did not.
