I put in another post after that where I specified why I think this will not come under the Contract Labour Act. Please see that and let me know if you agree. (It's mostly about the definition of establishment and the concept of intermittent work).
Assuming that I am right about it, there is the question of why the level of compliance verification can be relaxed. Note: I am not saying that compliance is not required. Compliance with all labor laws is required by the contractor. What I was referring to is the legal responsibility of the company to ensure compliance.
In the case of work done in the factory, the company as the principal employer is responsible for ensuring ALL the labor laws are complied with in full. The wording of the acts and the stand taken by the courts are such that the principal employer is liable for everything.
In the case of this particular CSR activity, it is being done in a place other than the factory. It is not an establishment under the Contract Labour Act; therefore, the principal employer is not supervising the activity or monitoring it closely (can't) since they do not have an active setup of managers, security, safety officers, grievance mechanism, etc.
Some basic and important things need to be monitored in any case (referring to my earlier post) like minimum wages, PF, ESIC, proper attendance. Since this is a large company (otherwise they would not be doing CSR) and a responsible citizen, they will try to ensure that workers are not exploited (again not strictly specified in the act). So they will send the safety officer from time to time to check if safety measures specified are followed, that work shifts are not more than 9 hours a day (or as allowed in the BOCW Act), that rest interval is provided. For this, they will check that systems and general practices are followed.
Let me take an example. Use of PPE - safety lines, hard hat, gloves, safety shoes. In a factory, they would be checking and ensuring that contract workers are wearing them all the time. If not, that person may be removed from work until they get their PPE. This they do not do because the act says it, but because in case of an accident, they will be held responsible and will have to pay worker compensation. By enforcing the use of PPE, they are minimizing the risks.
If the same thing happens at the school where repair is going on, and there is an accident where (say) someone is hurt because something fell on their toe and they were not wearing safety shoes. Will the company be held responsible? No, they would not. They will have to ensure compensation is paid, mostly from ESIC. But they are not directly responsible because the place is not under their supervision.
Take another case, let's say there are cases of workers being denied a weekly off, but the attendance register shows they are not working on Sunday. If this were in a factory, the company is directly responsible and will be answerable as to why they allowed it to happen, why they didn't prevent it. But if it happens at the school, the contractor will still be liable and answerable, but the company will be able to defend itself by showing adequate checks were put in place. However, since they are not present at the school, they could not discover that the attendance records were fraudulent.
I hope my point is clear. Please let me know your views, especially if your experience shows that my assumptions are wrong.