Consider the following thought experiment. A restaurant selling meals for $10 will happily accept payment in the form of one Hamilton bill ($10) or two Lincoln bills ($5). That is, the nominal exchange rate between Hamilton and Lincoln bills is 2:1. Now, suppose that the supply of Lincoln bills is increased but the supply of Hamilton bills remains the same. The exchange rate remains unaffected […] That is, the increase in the supply of Lincoln bills has led to a decline in the purchasing power of both Lincoln bills and Hamilton bills, even though the supply of Hamilton bills has remained fixed. Might an expansion in the supply of Altcoin have a similar depressing effect on the price of Bitcoin?
This is a bad analogy, because Bitcoin and alts are different currencies. If you look at market data, there's no precedents of Bitcoin dropping in price as the result of some altcoin crashing or an ICO attracting a huge amount of investment.
Bitcoin crashed because it was in a speculative bubble, people got euphoric and though that Bitcoin is going straight to $100,000, but it soon became clear that it was just another cycle, similar to those that happened years before. There's no need to come up with conspiracies or complex explanation when it's pretty clear what actually happened.
It's a terrible example because it assumes that the BTC/ALT price will remain static when history has clearly shown that not to be the case. It is also only assuming that the two things in consideration have one purpose only and that is as a currency.