It is. And, as a matter of fact, the inoculation of oak trees and truffles is a carefully guarded secret of the INRA (https://www.inrae.fr). There is no natural occurrences of truffles outside the south of France, Italy and Spain.

Not true: https://gastronomica.org/2008/11/03/truffle-wars/

> Chinese truffles (Tuber indicum), that is, a close relative of the French black truffle (Tuber melanosporum) [...] even ripe Chinese truffles are not wonderful [...] Although it doesn’t have the same powerful aroma or strong flavor, it’s a close approximation.

AKA, a cheap Chinese knock-off.

Those are stats for truffles and mushrooms combined. There is certainly less than a thousand tonnes of truffle production worldwide annually.