Drop across all crypto pairs at the same time on 4 X exchanges

Not being new to the world of FX but now in Crypto. Why in the crypto world do we see drops like this. Theoretically if the sell off was BTC only due to Koreas potential banning of exchanges then surley it would only affect bitcoin.
And if it only affected bitcoin all trading pairs against bitcoin should have gotten stronger (more bitcoin per token).

Why do we see them all drop at the same time ? Any ideas please let me know. My throughts are trading bots


Cya