Most “smart money” (large institutional grade investors) enter positions before the end of the day close. Their traders see what the intraday price action looks like and their traders typically like to buy below VWAP (nice bonuses happen if you can buy below your average position). If they are building a 100m (just an example number) share position — it may take 6-8 weeks to get to 100% of the 100m shares.
As their orders hit the market and get filled, they cause the stock price to trend upward and is exactly why they can’t put out a 100m share order all at once, it would cause their own avg cost basis to skyrocket, so they “tippy-toe” in over a period of several weeks until they are at their planned full size position of 100m shares. What you are describing in your question is the exact scenario where/when this occurs.
As you may know, the “market open” is wildly volatile, so even HFT’s (high frequency traders) avoid it — smart money plays in the afternoon once the choppy waves have subsided.