What insight does True Strike grant?


The part of the True Strike spell I am concerned with reads:

Your magic grants you a brief insight into the target’s defenses.

I’d always considered this to be flavor text. But a friend of mine disagreed. He argued that this meant that the DM should give the player some insight into the target’s defenses.

For example, the DM might say “You sense that the dragon is fortified against fire.”

The thing is, I’m not sure he is wrong. Is this interpretation correct?