Two wire at light switch
Other loads are getting you
Switched-hot@switch and switched-hot@lamp will read continuity because they actually are the same wire.
However, always-hot@switch and neutral@lamp will also read continuity because of other loads.
Presumably this is NOT a dedicated circuit just for that lamp.  So that means the circuit visits other lamps, other hardwired loads, other receptacles etc. If any of them are switched on, they create a relatively low resistance between always-hot and neutral.
So even though you have the circuit turned off, any loads attempting to draw current will create a continuity between always-hot and neutral.
However, if you use a proper voltmeter, the resistance will be detectable.  (mind you with incandescent lights and some digital power supplies, it can be lower than during operation; that's what inrush current is all about.)  For instance a heater drawing 12A will have -- let's see E=IR
 120V = 12A x R 

R is 10, so 10 ohms.  That's quite a low resistance value, so a continuity detector would read continuity, but a real ohmmeter should show a true number.