I presume the comments //1, //2 etc are part of the problem. They are probably referenced in the SO post to explain how the code works. It is not that they are especially harmful in themselves, but they serve absolutely no purpose in the production code. The fact that they were left in suggests that the code was blindly copied without being checked.

SO is a great resource for ideas about how to solve particular problems, but you need to fully understand the idea and preferably rewrite it yourself.

In the example given the code looks so boilerplate that there probably isn't any copyright issue. The problem is that the engineer copied it without checking.