Generally, overclocking can be achieved by either modifying the front side bus (FSB) speed or the multiplier.
The K only means there's an unlocked multiplier, so even for the regular Intel CPUs, you can overclock by pushing the FSB speed. Increase the bus speed allows for some overclocking, but it's less than changing the multiplier would allow for.
In any case, it sounds like you accidentally applied the automatic tuning that your motherboard allows, which slightly overclocked your CPU.
As for are you safe, most modern CPUs are pretty intelligent about clocking down or shutting down if they cross thermal thresholds or what not. The Asus tools are likely pretty decent at knowing/detecting what an acceptable limit to push your particular CPU is. If the system was stable, you probably didn't damage the CPU . . . you may have decreased it's lifespan somewhat, but there's no real way of knowing. As long as you're not constantly running the CPU at full speed (meaning the highest heat), and have decent cooling, the risk of damaging a CPU is low, even when overclocking via bumping the FSB.