I just found this article on Cointlegraph which said that on July 14 a spam attack was carried on the bitcoin blockchain.
This spam attack turned the bitcoin blocksize from 1MB to 3MB through invalid transactions.
I knew that spam attacks have previously been performed on the bitcoin blockchain but I never knew it could increase/decrease the blocksize.
Anyway, since the transactions were invalid and probably got kicked out of the blockchain, it didn't create any impact on the price.

Source: https://cointelegraph.com/news/spam-attack-bitcoin-average-block-size-suddenly-spikes-to-over-3mb