This line unwraps the list and passes each element sequentially to the nn.Sequential container.
If you would pass the list directly, you would get a TypeError:
my_list = []
my_list.append(nn.Linear(1, 1))
my_list.append(nn.Linear(1, 1))
my_list.append(nn.Linear(1, 1))
module = nn.Sequential(my_list)
> TypeError: list is not a Module subclass

module = nn.Sequential(*my_list) # works