That was a different event, the OTC sale of Bitcoin to Blackrock caused that. ETFs get discount for the volume they buy, driving down the price.

OTC, or Over The Counter is a term used for high value buyers such as ETFs or high net worth individuals or funds. They have accounts and phone up to negotiate their purchases. 

OTC is only available for buys over about $500K and typically is for buyers in the multi million dollar bracket. 

ETFs are spending hundreds of millions, so can negotiate bigger discounts.