It's a bad thing to happen if you have to pay for the repair.
But, as it has been done, no worries for you.
BUT, and it's a big BUT, most people are aware that cambelts need to be replaced for this very reason. If the seller had not replaced the belt by 115k miles, what else has he scrimped and saved on. Anyone who cares about their car will have had it changed much earlier.
I had a mate like this - bought a Mk4 Golf GTi, kept it for 2 years, spent zero on it and sold it. When I asked him why he was selling so soon, he reeled off a list of things that needed doing (inc cambelt) and said he never spent serious money on maintenance. SO he flogged it to some poor sod who got a car that had not been properly maintained.
Unless it was a case of real bad luck, it sounds to me like the seller had not been servicing it properly. Check the records - it should have been replaced around 5 years / 60k miles.