My only concern is the bad part. Did you tell them that there'll be storms? Did you explain that there's a bull run but sometimes a bear run? Because I am sure that you definitely not want them blaming you for any of their loss. Whenever I bring people to crypto or tell them about investments, I also let them know that it can be risky. I hope you did this, if not, you can still tell them while it's early.
Yes, you should have mentioned the time period for which they should hold this investment. You have bought all these coins at high current prices and if bitcoin starts dumping today, your uncle portfolio will be 30 - 40% down. He may not be ready to see this loss in his portfolio (although there is no loss if you don't sell in loss).
If he is investing for 4 - 5 years, then there is no issue and this is the best investment.