rpc: clarify getblockfrompeer behavior when called multiple times

src/net_processing.cpp

@@ -1439,7 +1439,9 @@ bool PeerManagerImpl::FetchBlock(NodeId id, const CBlockIndex& block_index)
     // Ignore pre-segwit peers
     if (!state->fHaveWitness) return false;
 
-    // Mark block as in-flight unless it already is
+    // Mark block as in-flight unless it already is (for this peer).
+    // If a block was already in-flight for a different peer, its BLOCKTXN
+    // response will be dropped.
     if (!BlockRequested(id, block_index)) return false;
 
     // Construct message to request the block

src/rpc/blockchain.cpp

@@ -781,7 +781,8 @@ static RPCHelpMan getblockfrompeer()
         "getblockfrompeer",
         "\nAttempt to fetch block from a given peer.\n"
         "\nWe must have the header for this block, e.g. using submitheader.\n"
-        "\nReturns {} if a block-request was successfully scheduled\n",
+        "Subsequent calls for the same block and a new peer will cause the response from the previous peer to be ignored.\n"
+        "\nReturns an empty JSON object if the request was successfully scheduled.",
         {
             {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The block hash"},
             {"nodeid", RPCArg::Type::NUM, RPCArg::Optional::NO, "The node ID (see getpeerinfo for node IDs)"},