I'm not sure how this furthers your point. You added $90bn and $50bn; the former assets held by the FDIC, the latter about the amount of deposits the acquirer assumed from the FDIC. That doesn't make sense.
It does make sense. The FDIC is holding 90B in assets from SVB. Those assets were purchased with deposits. First Citizens actually bought 72B in assets for 50B. So 72B + 90B is pretty close to the original 167B. Using 90B as an estimate, given that we know SVB bought those assets with depositor funds, does make sense if you’re just trying to make a rough estimate.