Progress is if multiple processes are waiting to enter the critical section and there is no process in the critical section, eventually one of the processes will gain entry.
Now first u executed S1 that is a statement of Process which implies that it wants to have access to the critical section so there is no progress issue if S2 has to wait ... Progress problem would have been there if for the execution of Process 2 Process 1 had to execute 1st that is alteration was required. Like this if we context switch anytime then we will always be having a progress problem for some or the other process.. So I think main aim is to check that there is no strict alteration and deadlock which implies progresss .