"401(k)" is a class of tax-advantaged account for retirement, theres no one global 401(k). If you are concerned, you can look at your disclosures or ask your provider.

All of this is kind of beside the point though, because the issue was leverage not exposure. In south korea ppl were forced to sell at the low point of the market due to margin calls. For a retirement account, you can just choose to take a disbursement next month or next year (assuming youve managed personal cash flow with sequence of returns risk in mind).