I can think of a few possibilities.
1. Non-Muslims are not allowed in a mosque? (I don't know the answer to this question.)
2. Local Muslims did not issue an invitation to the mosque?
3. Non-Muslims are too scared to go to a mosque?
4. The local political noisemakers did not allow the building of a mosque?
5. The Bishop is sincerely trying to make a gesture of peace?
6. To recycle an old pejorative -- "Fruits and nuts thrive in California?"
I think number five is closest to the truth. The release of doves is a distinctly Christian symbol of the Holy Spirit, but also a symbol of peace.
Reading from the koran by someone who has some understanding of the context might actually lead some listeners to a better understanding of what we have in common with some of our neighbors. I see that the priest from the Cathedral read from the Beatitudes.
Roses are placed on caskets at funerals, rose petals are scattered at weddings, roses decorate Churches at times. Once again, symbolic, but not liturgically significant.
I don't think the events described in the article rise to the level of "veneration", in the Catholic/Orthodox understanding of veneration of icons or the gospel.
I don't think this event was particularly useful, and would not have attended, but I don't think it is worth getting worked up over.