Agreed. The chain mileage seems reasonable, but it seems low to need a cassette replacement (although wet road grit can be a significant wear factor). Best way to tell is to put on a new chain and then go for a ride and see if it skips on the old cassette. If it does then replace the cassette, otherwise it's good to go until you replace the chain again. I just make sure I have a spare cassette available when I replace the chain so I'm not stuck without a bike in the meantime. Finally had to replace a chainring, but that was with almost 150,000 km on it