As has been explained in few articles that India, Iran and Israel is the nexus against Pakistan, so although it was a bit sudden news but is no surprise that right after Pakistan and China signed an agreement to develop Gwadar port, India and Iran have also signed an agreement to develop Chabahar port.
As can be seen that Chabahar is right next to Gwadar. I agree its nothing wrong to make agreements with other nations but the interesting point is that this agreement is signed just when Pakistan and China signed the agreement on Gawadar development. As they say there is nothing coincidence. This agreement also provides us an input that who will be interested in deteriorating the security situation in Baluchistan to stall the development of Gwadar and related activities.