With a fixed exchange rate, the choice of currency does not matter for Benford’s law.

Benfords’s law states that for many real-life numbers x, log(x) is uniform.

Converting to another currency using exchange rate E, so that y = E*x, yields log(y) = log(E) + log(x). This corresponds to a shift of the distribution of log(x) and does not change how uniform the distribution is.

However, if the exchange rate varies with prices, then it will matter.

The currency against which BTC is exchanged the most is very likely the one that shows the best fit (most perfect market). Assuming that currency is the USD I expect any other currency would result is an even worst fit

There are other problems with the article but currency exchange shouldn’t substantially affect the distribution.