No, it is not a mistake.
A similar confusion exists with the UK passport. Some argued that because the passport had the words "European Union" printed on the cover then it was an EU passport and that it could not be used after the UK had left the union. At various meetings in France hosted by the British Embassy the officials were at pain to emphasise, over and over, that what is printed on the cover has no legal standing. That which is printed on the inside pages does and on the inside pages of a UK passport there is no mention of the EU, only the United Kingdom.
On the cover of UK pilot licenses the words "European Union" and "issued in accordance with Part-FCL" are printed. The main title is the "United Kingdom Civil Aviation Authority". There is no reference to the European Union on the inside pages of the UK issued pilot licences. On the UK licenses issued prior to EASA the words on the cover are "Issued in accordance with ICAO standards", so a similar convention only.