You turn off the connection, reopen a website and still see a working page. That does not necessarily mean the device is secretly online. A service worker can help the site respond using resources previously stored in the browser.
MDN’s client-side storage tutorial demonstrates an offline example that stores page resources through the Cache API and uses a service worker to answer requests. The behaviour depends on what the developer implemented and what has already been saved.
A visible page is not proof of a live connection
The page shell may load while fresh messages, account changes or new searches still require the network. A saved article might remain readable, while a form cannot complete its submission. Treat each function separately rather than deciding that the entire service is online or offline.
For a harmless check, use a page that does not involve payments or important submissions. Load it normally, disconnect, and try reopening the same resource. Then try a resource you have not visited. Note the difference without assuming every failure is caused by the same mechanism.
Read status messages before repeating an action
If an app says an action is queued or waiting to sync, do not treat that message as confirmation that the server has received it. Reconnect and check the service’s final status. Repeatedly pressing a submission button can make an uncertain situation harder to interpret.
When troubleshooting with support, describe what remained visible, what stopped working and whether the page had been opened earlier. This is more useful than simply saying the website worked “without internet”.
Clearing site data may remove useful offline material or unsynchronised work. Check the app’s own guidance and save important work appropriately before using that step as a generic repair.
Offline capability is a design feature with boundaries. Understanding those boundaries helps you distinguish a saved interface from current server information—and prevents a reassuring-looking screen from becoming the only evidence that an important action succeeded.