Recent Japanese earnings reports have been notable for worse-than-usual selloffs in companies that miss expectations. To veteran market players, it’s a telltale sign of an influx of "tourist investors.”

Companies that missed analyst forecasts since the start of the current fiscal year in April have seen share-price drops of about 6%, 2 percentage points more than the average over the past 10 years, according to an analysis by Rie Nishihara, chief Japan equity strategist at JPMorgan Chase & Co. In contrast, reactions to beats have been in line with the historical average, she said.

Seasoned pros think the bigger declines stem from disappointment among traders who are relatively new to the market and may have unrealistically high expectations. In particular, they say many global investors are dabbling in Japanese stocks for the first time or after very long hiatuses, often as an alternative to slumping Chinese equities.