I always believed he was a Romulan transmitting information from the future (Daniels would later tell Archer that Future Guy was from the 28th century, three hundred years before Daniels' own time), which opens all sorts of possibilities as to what his agenda really was now that we know that Romulus is destroyed by the giant supernova shockwave in 2387 that also sets the Abrams timeline of the new films into motion.
Perhaps Future Guy wanted to prevent the destruction of his homeworld and decided that tampering with Earth and Klingon history prior to the birth of the Federation would lead to the disaster never happening, with the added incentive of an Earth-Romulan War with a different, more favorable outcome for the Empire, thus saving his world and making it even more powerful at the same time?