It is possible to get sucked into studying openings at the expense of studying other areas of the game and I think this is where the advice not to study openings comes from. I've seen advice such as only use 20% or so of your study time on openings and so on.
But I'd be very surprised if someone were to advocate "no" opening study or knowledge is required to improve at chess. This then leaves us with requiring "some" opening knowledge to progress and this leads to confusion as we now have to clarify what is meant by "some"
If a GM talks of some opening knowledge they may well be referring to the knowledge that say a typical RHP 1800+ player has.
I willfully ignored the advice not to study openings and I'm not unhappy with where I'm at (I enjoy the study!) but I now agree that I'd have had more improvement if the time had been spent on tactics and endings.
In my 15 or so competitive OTB games in a year there's a possibility that I'll never play one of my most studied opening lines. Once or twice I have "won" the middle game but been unable to convert this into a winning endgame due to lack of endgame knowledge.
Here on RHP I have books and databases and on several occasions have been quickly outplayed on leaving a book line where I was supposed to be better. More tactics and strategy training may have solved this.
The other consideration is that opening theory is such a vast topic (one valuable lesson learned from opening study) that an amateur with just a few hours a week of study or playing time isn't ever going to cover sufficient ground to impact all that much on the results by comparison with spending the same time on tactics and endgame.