He's only saying that the investment in the miner was bad. Not the investment in BTC.
Why would a 100% ROI would be considered bad?
Do you also not understand the grammatical difference between bad, worse and worst?
I will try one more time to explain.
If you had $7000 to invest in BTC,
you have 2 choices. You can invest directly at the current exchange rate or you can invest in a Jupiter for a predicted amount of BTC over a period of time. Those are your two choices. Both have the risk of the exchange rate changing. Investing in a miner has an added risk of delays/difficulty increases. You should only choose to invest in the miner if you believe it will mine more BTC than you can purchase. If your miner made less BTC than you could have purchased directly then you made the wrong choice. The fact that you still made a fiat profit is great but it was not because you decided to invest in the miner but because you decided to invest in BTC via the miner but for a worse rate than you could have gotten on an exchange.
No, you had an infinite number of choices on how to invest your money. Why single out buying BTC as the only other alternative to buying a miner? You could of, just as easily said, buy 7200 lottery tickets or buy shares of Facebook. Many, many investments could have been better or worse than buying a miner. Pointing out that buying BTC would have been better is not only obvious sitting here today with BTC at $240 but doesn't prove that buying a miner was a bad idea.
I personally did buy BTC directly as well as buy a miner and I lost my shorts on the direct BTC investment. Sitting here today, I know I should have just held it but I sold for a loss of ~30%. When you say "you should have bought BTC instead of a miner", what you are really saying is "you should have bought BTC on the day you bought your miner and used your powers of prediction to delay selling it until today."