The point is, the Gurus infused light into humanity. If the website has the bias to call the humanity -->
'Hindu Dharma' , why not have the heart to accept their bias and understand their point of view. Maybe to the hindus, Guru Gobind Singh did save them.
Does that make you more of a hindu? Does that change your preception of Sikhism?
Just understand that this is a website with sources that might be biased.
Instead of complaining to the web author, why not write a letter to suggest to say something like
" Guru Gobind Singh infused a new spirit into Humanity"
Thats all. But it seems your anger is based on your hatred for something else.
Again, I suggest that instead of lashing out, take the time to think over what you believe and how you can help instead of calling people idiots.
Best wishes,