I think the problem he has with the word is data is the plural(!) for singular datum. So one data is datum, two cactuses are cacti, and two datas is data. Maybe not always colloquially but technically. Hence anecdatum and anecdata.

It depends on where you are. In the US it's like you say. But in the UK for example they will often use data as singular.

"Datum" is rarely used in the US, unless you want to sound pretentious. (This coming from someone who cringes every time "who/whom" is used incorrectly.) We use "data" as an uncountable noun.