Was this true in all of their games? I know early PlayStation games did use O for confirm and X for cancel - even a few years into its lifetime, this was the case as Final Fantasy VII is an obvious example.
Are you talking about the Japanese version of Final Fantasy VII or the western version ? I have the Japanese version at home, I can check quickly if needed.
Both versions use O to accept and X to cancel. In the european FFVIII hovewer it was switched around. I think only early and rushed ports of japanese titles used O to accept on the playstation.
It's still true today, for instance dark souls on the ps3 uses O to accept on the japanese version and X on the western.
I'm still not sure why Sony did that by the way. While I'm willing to believe that X strongly means "bad/false" in japanese, I don't feel like it really means "accept" in western cultures as far as I know. When the playstation came out I don't think I would have had a lot of trouble accepting O for accept and X for cancel.
It depends on the version of the console. Japanese Playstation Portable and Vita have the O button as "accept" - but I have noticed that not all games respect that. European games played on a Japanese Vita will use X for accept, but on the Playstation Portable most games will use the system settings, rather than their own(there were exceptions, however).