Yes, this was rude and unnecessary to some extent. A lot of the art of diplomacy is hearing out the other side's view, even if you know deep down that it's worthless. But to be fair, this wasn't the US mainstream being snubbed here. Delahunt is not particularly popular, and his political views are (on the US spectrum at least) fairly extreme, certainly not near the mainstream. A congressional tour led by J Street is not the same as a visit by the Secretary of State or the President. The policial momentum in the USA at the moment is against folk like Delahunt. If J Street is mostly attached to such elements, which are rapidly sapping support, then Israeli interests are safe for now.
Egypt to hold parliamentary election in 2 phases starting Oct 18-19 (Reuters)
from the article: U.S. lawmakers in Israel 'puzzled' by Ayalon boycott