Earlier I was viewing my HTML document, but when I opened it this popped up. Musdguest is the name of my school's WiFi, and this kinda looks like the source code for my school's website...?

Just stalked your profile. You seem amazing 😅
About the response, that could be some faulty router configuration/code.

That's a captive portal login page. It will intercept any HTTP (not HTTPS) request and reply with that page, which is a challenge for some credential (in hotels, this is often your room number -- for a school it might be your student ID and password).

The page will POST those credentials to somewhere that the captive portal is listening, and once it receives a satisfactory request, it will allow traffic from your device to pass.

Occasionally, you can find ways around this. For example, some will allow ICMP or DNS packets through, so if you had a VPN listening on the right port, you could tunnel traffic right around it.

@DjSall
Thank you :)

@tullo-x86
Ahh, I understand now. Thank you for the explanation!

@ignuit
SL kinda sucks now :)
I'm not sure why they did haha.

@Condor
I'll do that now. Thanks.