The cable from Tbilisi ends with the suggestion that Georgia make "public and/or written commitments about the exclusively defensive nature of its new military programs" and suggests inviting Russia to sign a "non-use of force agreement." In contrast, the cable from Moscow concludes the U.S. cannot say "yes" to a "significant military relationship with Tbilisi" because Russia will increase tensions in the region and engage in "more active opposition to critical U.S. strategic interests."
To further contextualize the two cables, on November 20th of this year President Obama met with Georgian President Mikheil Saakashvili and pledged to contiue U.S. support for Georgia's bid to join NATO (which Russia opposes). Saakashvili said President Obama explicitly indicated support for Georgia's "territorial integrity" and the White House press service said, "The two leaders discussed the Georgian government's efforts to implement political, economic, and defense reforms and our shared interest in securing democracy, stability, and prosperity in Georgia," which, because of the cables."
"Defense reforms," of course, is a euphemism for arming the country to defend its "territorial integrity," which means being able to function as a democratic and economic model for other countries in Eurasia. (The cables allow people to understand the meaning of all this diplomatic jargon, which normally just flies over most American's heads because they don't know what the jargon is referencing. Now, one can know what Obama means by "territorial integrity"; it's very comparable to the idea of a country having a "right to exist.")
Overall, what this shows is that both ends are on some level being played against the middle. The U.S. knows its arming of Georgia will bring escalated tensions with Russia, but it can use the support from the country in prosecuting the "war on terror." The U.S. knows respecting Russia's wishes to not have the U.S. meddling in the region could be a win for Georgia in the long-term, but the U.S. does not want to be seen as letting Russian interests discredit the validity of U.S. interests in the region. So, the U.S. attempts to argue Russia is using propaganda when it suggests the US is arming Georgia, and the US attempts to convince countries that the military cooperation is purely aimed at helping Georgia defend itself and not wage war against its neighbors.
All this assumes Russia will allow Georgia to defend itself and not see an increase in defenses as a threat. If this were Iran, Israel would be allowed to legitimately argue that escalating defense spending was seen as preparing the country for war. After upping defenses, the country would be able to mount attacks and protect itself from repercussions. So, one can see why the U.S. might be suspected of turning Georgia into a country that will just create more trouble in the region; plus, clearly, U.S. is prepared to use Georgia as a proxy to advance its interests and that makes Russia leery of U.S. involvement.