@Sahil2 That’s a good question.
UEFA UCL Round 16 rules take precedence in this situation: Teams from the same group or country could not be drawn to face each other .
During the draw, the last two clubs in the Runners-up bowl were Inter and PSG. When Inter was drawn, there was only one possibility for Inter and that was to draw against Porto as you rightly said Inter and Bayern were in the same group earlier.
With PSG as the last one remaining, it was set up against Bayern.
Here is the link to the UCL Round 16 Draw Replay (You can watch 17:58 min onwards for the last 2 draws - Inter and PSG)