This has always bugged me.
Shouldn't it be sync 1->2 as it appears to be syncing oscillator 1 to the freq of oscillator2?
You should probably read it as "Osc2 syncronises Osc1" therefore Sync 2->1 ... but yes... I've been wondering about this from time to time as well... in my own editors, i usually just call the button "Sync", and place it within the Osc1 section.