Yes you can just say that.

1. If someone knows for a fact that you have Monero and they know the exact amount, and want to know where it came from:

   • Move them to a new wallet
   • I mined these coins a very long time ago, I do not have the mining equipment anymore
   • Also the wallet I used to mine them was on an old computer that got infected so I moved all to this new wallet

2. If someone suspects that you have Monero but does NOT know how much:

   • Imagine you own $10k in Monero
   • Move a small amount to a wallet ($200??)
   • If authorities ask you how much you have, show them the wallet with $200.
   • Go back to scenario 1 (I got those 200 from mining a long time ago etc etc)

3. If no one suspects that you have Monero, and for now you are “in the clear”:

   • Follow good opsec
   • Do not tell anyone that you have Monero
   • Do not exchange that Monero for fiat using KYC services. Always use something like Haveno, or use the Monero to buy prepaid cards anonymously to use in shops
   • If someone starts suspecting that you might be using Monero but does not know how much, revert to scenario 2

Of course it is better if you avoid anyone knowing you have Monero altogether.

Remember that you always have the option of moving them to a new wallet, say you got hacked and have no access to it.

Of course all this depends on your country and how authorities are there. If you live in a very authoritarian area where authorities do not care about evidence and they only care that “you look guilty”, nothing will save you. If you live in a country where you must go to court and be proven guilty, I think with Monero its pretty easy to do any of those steps and cover your ass.

But as always, try to not be discovered using Monero in the first place