Usually, EXIF will only report flash use reliably when the camera can communicate properly with the flash. On Canon bodies, that generally means a Canon or E-TTL-compatible flash/trigger connected through the hot shoe.

If you use a non-Canon flash, a non-E-TTL trigger, or a connection that does not pass Canon flash communication, the camera may still record "Flash: Did not fire" even though the flash actually fired. The same can happen with some trigger setups or PC-sync connections.

So in practice:

• Canon / E-TTL-compatible flash: EXIF often correctly shows that flash fired.
• Non-E-TTL or manual-only flash/trigger: EXIF may incorrectly say "Did not fire."

Lightroom may also be showing only a limited flash field, so checking Canon’s own software or a fuller EXIF viewer may reveal more detail. But if the flash system does not report its status back to the camera, the metadata cannot reliably confirm that it fired.