I think some Alts drop the price too and many good alts drop the price more than 80%. I think its the same with bitcoin because as main currency in cryptomarket, its affecting to most altcoin price in market.
I think what the OP was saying is that within a seven day timeframe the price of bitcoin dropped by more than two other coins in percentage terms. I don't believe any comparison was being made with other coins or longer timeframes.