Blocked websites on macOS host but not on Win7 virtual machine In China there in the Great Firewall which blocks i.e. youtube. Fortunately in my university in China someway they provide access to youtube, so students can use youtube by means of campus wifi. I noticed on macOS I have to keep IPv6 configured to Automativally so it works (I can access youtube) most of the times. 

Sometimes (very frequently) even with that configuration I cannot open youtube. I also noticed my Windows friends has much less of this problem, in Windows youtube works almost always.

Then I tried to run Windows 7 on a parallels virtual machine on macOS and bingo. Chrome in the vm loads youtube nicely.

On macOS host I tried Safari/Chrome/Firefox and none of them loads youtube.

How can this be explained?

I'll mention that I need to login to the wifi via captive portal, not sure if that matters.
The firewall might be blocking dynamically, and if so, it could decide on a large number of factors that are hard to guess or summarize. 

For example, firewalls can tell what platform you are using, as well aspects of the network configuration.

What you describe could be summarized as: based on the assumption that Windows is blocked less from YouTube than macOS, your computer is not being blocked for its location on the network, but usually because it is running macOS (in this specific environment). If that same network device was running Windows (or more specifically a Windows-based browser), YouTube works, in this specific case.