Chains age by miles, not by months. And riding conditions do play a big role. And the more gears in the rear the thinner the chain and the faster they wear. But it sounds short. My all-year, all-weather commuter probably go 3000 miles on one chain.

Maybe your mechanic used one of the bespoke chain stretch rulers, which some people don't like much.

I don't notice much difference WRT chain brand. Frequency and diligence when cleaning and lubing seems to be far more important.