Sorry for the delay in getting back to you. Computer problems . . .
AS to your question - If he is expert, why he sold lessons, If I understand you correctly, you will not loose by teaching others to do the same. The Forex market is over 5 billion dollars (20 times the size of the stock markets), so what we trade in the market will have no influence on the market, so no reason not to.
Also, They are not just teaching theory. They are teaching what they are doing. Some will even show you live what they are doing. They are not just talking.
If you want to learn about forex and crypto, You want to learn from an expert. If you are learning from someone who just has some nice theories, you there is no proof that what they are teaching is valid in a real market. If you are learning from 8 figure traders, you are learning from what they are doing to earn that and you can then use what they teach you to use the same methods to trade your accounts also.