I just want to understand why the wallet program displays incorrect information that is not contained in the downloaded wallet.dat file
why does the wallet program inherit information from the previous wallet?
because we know that there is no such transaction on the network and the wallet.dat file has been replaced.
I'm not sure why it is showing a transaction from
your wallet when you are loading a completely different wallet.dat... Are you sure you stopped Bitcoin Core first, and then replaced the wallet.dat?
If you swapped the file first, then restarted Bitcoin Core, it might have done some "weird" things (like writing cached transactions etc to the replacement wallet.dat when you shut down Bitcoin Core and then restarted it), but I would expect that it would most likely just corrupt the wallet.dat and it would fail to load.
Either that, or you've somehow managed to accidentally import your address or private key into the other wallet.dat(s) by mistake.
The only other thing I can think of, is that mempool.dat is somehow holding onto "your transaction", and when you start up with a different wallet, it adds that transaction to that wallet, thinking that it is "yours"?
But that is just pure speculation...
Maybe do as BitMaxz said, delete the mempool.dat when you change the wallet.dat files and see if that stops it from happening.
Maybe wallets with 70 and 78 coins are fake? Did one client send them to me.
Is the wallet program showing strange transactions for this reason?
That is, the program works correctly, but if the wallet is fake, then we will see this or another anomaly.
It's quite possible that a fake wallet would show "weird things", depending on how it was modified... it's also possible it's NOT a BTC wallet, but an altcoin wallet (like LTC or DOGE etc) and is showing "non-existent" transactions because of that... the transaction doesn't exist on BTC blockchain, but it exists on a different blockchain and was stored in the wallet.dat history.
However, that doesn't really explain why these wallets are showing a transaction that you say is from
your wallet.dat!!?!