NCAA rules. I observed a DPI called where the defender fell down in front of the receiver causing the receiver to trip and fall. Clearly, there was no intent to obstruct, just accidental.

I re-read the rule book and it says that the DPI requires a deliberate attempt to obstruct the receiver. Is intent required for DPI (or OPI for that matter)?

The way I read the rule, the contact has to be deliberate with the intent of keeping the opponent from catching the ball. In your situation, all other things being equal, I would not throw the flag. That being said, PI is hard enough to call on the field, much less through a brief description of the play. There are any number of factors that would change my answer.

Intent is required and it must be obvious. Based on your description of the play I do not see pass interference. Sometimes these collisions are so ugly guys feel compelled to throw the hanky, but they should not if it was not DELIBERATE.