Was police not allowed to go there? That is the only thing that would make it a no go area.
what I understand is that trouble started when aal e Sharif started removing barriers from TuQ's residence, even though they were provided after LHC order. So problem was not about no-go area but removal of barriers.
Even after that massacre, Sharif family is still not satisfied. They are causing all sorts of hurdles in his arrival.
So it looks like this talk of no-go areas is an attempt by Sharif family to justify their massacre.
There are no Karachi style 'no go area' in Lahore, and this is coming from someone who had fiercely criticised SS in other threads. However, there is a serious VIP culture in places like Model Town where certain houses belonging to politicians or people like Tahir ul Qadri have placed extensive barriers and strict no entry policy on the basis of security, similar to how you have barrier outside Bilawal Palace in Karachi or elsewhere.