ICNEA is a channel manager for accommodations, so it's natural that they ask for that information, as every host is legally forced to do so in most of Europe (Article 45 of the Schengen Agreement).
At most, you could have refused to give that information through the website and give it directly to the host instead, since you were already in contact with them. Although, I don't believe that small difference is worth the trouble. ICNEA seems trustworthy.