You're generally correct. However, you're not accounting for any MM participation in the trading.
In order to keep the market liquid, an MM may sell shares short (real or borrowed) at the ASK and then buy back shares (at a lower price) to cover at some later time. They also buy shares at the bid in order to cover previously opened short positions. Actions by MMs makes any assessment of buying and selling volume even more convoluted than you suggest.
For highly liquid tickers the short volume ratio is usually around 50%. The fact that the short volume ratio was only about 25% indicates to me that there was indeed more retail buying compared to retail selling.
But like I said, these are merely indications and cannot be precisely defined.