The day after the announcement, crypto influencer "Cobie" wrote on Twitter, "Found an ETH address that bought hundreds of thousands of dollars of tokens exclusively featured in the Coinbase Asset Listing post about 24 hours before it was published, rofl". The wallet had spent around $400,000 on multiple currencies listed in the announcement, which certainly appears as though they knew about the contents of the announcement before it was published.
This is not the first time allegations of insider trading have been made based on Coinbase announcements. In February, a trader made a profit of over $700,000 by trading on what appeared to be advance knowledge of two upcoming Coinbase announcements.