doc: update NeedsRedownload() comment

src/chain.h

@@ -178,7 +178,7 @@ public:
     //! Verification status of this block. See enum BlockStatus
     //!
     //! Note: this value is modified to show BLOCK_OPT_WITNESS during UTXO snapshot
-    //! load to avoid the block index being spuriously rewound.
+    //! load to avoid a spurious startup failure requiring -reindex.
     //! @sa NeedsRedownload
     //! @sa ActivateSnapshot
     uint32_t nStatus GUARDED_BY(::cs_main){0};

src/validation.cpp

@@ -6014,7 +6014,7 @@ util::Result<void> ChainstateManager::PopulateAndValidateSnapshot(
         index = snapshot_chainstate.m_chain[i];
 
         // Fake BLOCK_OPT_WITNESS so that Chainstate::NeedsRedownload()
-        // won't ask to rewind the entire assumed-valid chain on startup.
+        // won't ask for -reindex on startup.
         if (DeploymentActiveAt(*index, *this, Consensus::DEPLOYMENT_SEGWIT)) {
             index->nStatus |= BLOCK_OPT_WITNESS;
         }