Well there is no way Infinity War would make more money domestically then overseas so that is a very poor example.   But I stand by what I said earlier if a movie makes less then 50% of its total box office from overseas then it under-performed overseas especially if it was released pretty much in every major overseas territory like Black Panther was.  Even most movies that bombed recently managed to make more then 50% of their box office from overseas.

Then, you would be wrong.  If you want to say anything, it overperformed in America because of the cultural impact it had.  The last standalone film we got in the MCU was Thor 3.  If the BP continues outperforming the Avengers by 11.2%, and the FBO percentage holds, it will make ~$652.79M at the FBO.  This would mean it outperformed Thor 3 by 21.1% at the FBO.  Seems impressive, right?  Now, look at the DBO.  BP probably has another ~$20M+ to make, but it has already outperformed Thor 3 by 114%, and looks to finish 120% over it.

Ladies and gentlemen, the 'optimist/pessimist' dichotomy, personified. 

Optimists tend to see it as it OVER-performed domestically, while pessimists look at it and say it underperformed internationally. 

In reality, it did amazingly well, is one of the top 10 grossing films of all time, was a bonafide cultural phenomenon, has outstanding reviews, and is a smash hit no matter what angle you look at it. Only a negative person would look at this and try to find a way to devalue its success. 

Don't be a pessimist, you'll only end up sad. 

Well it looks like Black Panthers overseas run isn't over yet it will be the first movie to be shown in Saudi Arabian theaters in 35 years. But speaking of under performing and over performing. Ready Player One definitely over performed overseas since it made 75.8% of its box office from overseas and all the 80s references in that movie where mainly aimed at the domestic market.

Only a fool would only look at one aspect of something. The reality is that it did very well but also underperformed internationally. The reality is also that the ticket price in the US is now 15% than when The Avengers came out, for example.

What are people referring to when they call this movie a cultural phenomenon? Why is it a cultural phenomenon?

The problem with your premise is that Black Panther has over performed in both Foreign and Domestic markets. It has just over performed more in the US. The 640 million it's pulled down globally so far is close to the overall expectation for the movie.

Is it timing or did they pick Black panther for a specific reason?

It was coincidental, as there has been a massive push for women's of late.

Thank you. I'll be curious to see how many people there go to movies if this becomes normal in Saudi Arabia.