First off all it was publicity. Secondly, Jeffries retired in 1905, far before Langford's prime years of 1908 - 1912 ... I'm sure he would have loved a shot at the Jeffries Johnson fought and would have knocked him out much earlier ..
Jeffries was many things but he was not a Chuvalo type fighter. Like many fighters of this period our contemporary impresions of him are formed mainly by people who did not see him fight. When you get into the detail of it a diferent picture starts to emerge. Jeffries was cat quick for a man of 220 lbs and had reflexes like a rattlesnake. He also developed into a good technician later in his career and was verry methodical. He also did some interesting things like switching from orthodox to southpaw.
Jeffries has a reported KO win over Martin, which can be read in news papers. Martin was a solid boxer, but he could not take shots to the head or body well. It should be noted that Jeffries floored Hank Griffin multiple times in a four round match as champion...the same Griffin who defeated Johnson. Johnson could not beat Griffin in three full matches, let alone floor him, which is something Jeffries easily did. I do not think Johnson was as good as he would get by 1905. Remember, Johnson had a high stakes fight with Marvin Hart in 1905. The winner was a possible defense for Jeffries. Johnson floundered and failed to impress in the Hart fight. So what chance would he really have vs a prime Jeffries? Not a big one if you use the results of the time as a benchmark. Jeffries would have beaten Hart almost as easily as he defeated Munroe. In fact, Jeffries said if the public wants to see him fight Hart, he would do it. The money was not there, so Jeffries retired.