I'm afraid you have to revert your correction.
The very large majority of the words ending in -en are pronounced /ɛ̃/ and the rest are pronounced /ɛn/ (e.g. amen, cérumen, golden, hymen, lichen, pollen). An obvious and possibly unique exception is the preposition or pronoun en always pronounced /ɑ̃/.
The most common pronunciations in France are:
[ilafɛ ynɛʁœʁ] (ilafè unèreur)
[ilafe yneʁœʁ] (ilafé unéreur)
The liaison is possible [ilafɛtynɛʁœʁ] (ilafètunèreur) but extremely rare in casual French and still uncommon in formal French. An exception would be a French language teacher providing hints to schoolchildren during a dictée.
When the ...
Les liaisons sont distinguées en trois groupes : obligatoires, facultatives et interdites.
Après et la liaison est interdite.
Ils ont une fille et un garçon (pas de liaison).
Attention ! Indication du pluriel (avant et)
portes et fenêtres (pɔʁt-ze-fənɛtʁ)
To answer your questions, there is now only one acceptable pronunciation of européen in /ɛ̃/ but there used to be a pronunciation in /ɑ̃/ alongside the other one.
In the "langue savante", some words ending in -en or -ien were pronounced either /ɛ̃/ or /ɑ̃/ until the 18th century when /ɛ̃/ replaced /ɑ̃/ altogether. The words concerned were names of peoples ...
Dictionaries are right to claim it's /ɛ̃/, but the realization of this phonem varies between France (where most francophones live) and Canada (also home to quite a few francophones, but whose variety of French shows quite a few distinct features that sets it apart from the cradle of the language).
The specific set of French phonems /ɛ̃/ and /ɑ̃/ were ...