Fiatleak is just marketing bullshit, nothing more.
There's no way for them to know when fiat is entering market, they just use trades on exchanges and market it as fiat going in.
Please elaborate, isn't trade basically fiat going in regardless of what fiat comes out?
First of all, many people have signed up for many exchanges all over the world. And many exchanges use USD even though they are not located in the USA. So correlation between the physical location of the owners of the accounts and the exchange location and currency unit is dubious at best.
Secondly, someone can CNY with BTC (fiatleak triggers), and then turn around and sell it tomorrow (fiatleak triggers, because someone ELSE bought your BTC with CNY). So what fiatleak shows is just the volume of currency trades. It cannot actually show BTC being bought for a particular currency and then removed from exchanges which is what the term "fiatleak" implies.
The website is just another way to show volume with a name that is a catchy-meme but is actually complete bullsh*t.
In fact, since every buy is matched to a sell (neither currency is "consumed"), the entire premise that fiat currency "leaks" away and is lost is silly. Really the measure of societies' adoption and valuation of a currency is quite simply that currency's price, or more accurately its total buying power (market cap).
A million individual decisions that BTC is worth more than X dollars to an individual, then X+1 to someone else, X+2, X+500 dollars is what causes the value of a currency to change relative to another. And at all times those who have already bought BTC make the decision that the BTC they bought for X dollars is in fact now worth more than the X+500 dollars the currencies are currently trading at. The only way to track this is to see that the price has risen to Y and in fact is not going back down...
Its totally fascinating to see these 3 essentially completely abstract entities (fiat currencies, gold, BTC) pitted against each other in the currency war we call "price discovery". Gold, USD, and BTC are all arguably FAR detached from their "intrinsic value". Gold's use in electronics, etc is minimal, in fact by "intrinsic value" silver should be worth more. All use as a shiny metal in jewelery, etc is referential to its worth as a currency. Otherwise plating or paint would be fine. USD and other fiat currencies are backed by the "full faith and credit" of nations deeply in debt and controlled by a group that feels that printing a lot more is a good idea. Given this context, you can see that BTC just wipes away these fictions, proves that the concept of intrinsic value is useless (by its very existence) and simply excels at being a currency.