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.
And that over-simplification is why people are pushing back on your "explanation". Your explanation relies on someone having $7000 cash sitting someplace that could readily be converted into BTC or purchase a miner at equal cost in terms of time-value of money. Many people purchased a miner with a credit card at or near zero percent interest, where as getting a cash advance would have entailed a 20% or higher interest rate (typical of the cards I've seen, YMMV) in addition to a upfront fee. In addition, the miner itself retains substantial residual value for quite some time (if the ASICMiner gear is any indication) which is not being added to the equation (capitalization versus straight expensing of equipment for you accountant types out there) which further muddies the water of overall profitability. Especially when tax considerations are taken into account with same-year full expensing of business-related computer equipment being allowed for small businesses.
So, yes, in hindsight buying BTC would have been a *better* investment if one was to measure the progress of BTC mined as of RIGHT now versus selling bought BTC...but it hardly means that buying a miner was a *bad* investment considering that the miners have yet to reach their full potential of mining production AND they may yet have some to-be-determined residual value even after that which can be re-captured. While buying BTC will likely prove to have been the most optimal investment unless for some strange reason the diff increases start to level out....the margin of how much better is still very much in question at this point.