Could you elaborate, would like to know
It's only true insofar as Visa/Mastercard cards at payment terminals which accept Visa Paywave and Mastercard's contactless.
American Express cards typically require that the merchant also accepts Amex. Same for Discover. Though I'd wager most places in the US accept either none or all 4 by now, it's not everywhere.
Then it gets more difficult with certain countries where Visa/Mastercard aren't the predominant banking networks. Contactless is huge in Japan, but it is Suica and the iD and QUICPay networks. Visa/Mastercard often don't work there, special payment terminals are needed to handle all the different standards and the demand to do that for foreign banking networks that are comparatively small is low.
And then there's China. There are millions of contactless terminals, and they all run on UnionPay Quickpass. Banks don't issue non-UnionPay cards to be used domestically. Foreign cards used to work in Mcdonalds/Starbucks but I think that may have been disabled. Apple Pay in China is fundamentally incompatible with apple pay in the rest of the world. If I go to HK and say "Apple Pay", the transaction (which is looking to use Visa/Mastercad/Amex) fails. If I say "Quickpass", it works (but is a bit inconvenient because I have to enter my pin; on the flip side the way it is set up means that there's no transaction limit IIRC). The number of Quickpass enabled terminals outside of China is very limited, though.
Apple has never officially supported or even suggested using a card outside of the country of issue, and for good reason. "Apple Pay" is a bunch of things that run on a very messy mix of loosely-connected services. You could easily break it up into: "Apple Pay US", "Apple Pay UK, Europe", "Apple Pay Japan" and "Apple Pay China". There may be some overlap between the first 2 with respect to the major payment networks, but it can't be guaranteed to work in Japan since cards are set up primarily to work domestically. And it can be guaranteed not to work in China, just as Japanese Suica won't work in the US.