Not sure which particle your were thinking of but the axion was supposed to be really light, in the eV range, its the gravitino
that is in the plancks (need a atom smasher as big as the solar system) mass range. String theory does have axions in it as well
as stacks of light neutral particles called moduli. The article didn't say how they knew or why they thought that particle was an
axion. The experiment found at light neutral particle with mass ~19 Mev (or maybe 7 Mev) that decays to electron positron pairs, they didn't say the had a spin measurement, if its not spin 0 with negative parity its definitely not an axion. Another experiment (PVLAS) last year found evidence a particle with mass in the milliEv range, that fits more with an axion. So maybe this is something
else.