In my own opinion, investing in bitcoin is not a mistake because a lot of people given a great opportunities because they invested in bitcoin that they started to earn good profit from it that their investment really grew in only a few years. A lot of people are scared to invest in bitcoins because of it's risk, but bitcoin is still profitable as long you have patience and you can control your emotions.
Well, if he can answer his own statement now then good for him, now that the price of Bitcoin continues to rise and still increasing it is his time to tell if he really did a mistake, or he will thank himself and everyone for introducing crypto into his life which made him a lot of profit.