When you see a number that looks unreasonable based on your assumptions (how many books would he publish a day if that were accurate? What percentage of books on Amazon would he have published?), it is often useful to challenge your assumptions and ask if there is another way to frame the statement that makes more sense.
If English is not your native language, this can be subtle and catch you off-guard. I know that.
However, to "sell over 250,000 [...] books", would idiomatically be considered a number of copies, not a number of distinct titles.
Your response comes across - completely unintentionally, I presume - as a little obtuse in the "being slow to understand" sense, and if this is something you find others commenting on you might personally benefit from doing some work on it.
