Strettle may have thought he felt the ball touching the ground, but there was obviously at least one arm underneath it,
From what I could see (on the TV replays) one of the arms beneath the ball was Strettle's own. The ball (if it touched down over the line at all) was supported by Strettle's wrist, making it very difficult to assert that he was 'applying downward pressure' to the ball.
As to whether England could have equalised, if the try had been awarded, Law 5.7 (f) states that: "If time expires after a try has been scored the referee allows time for the conversion kick to
be taken." Quite clearly, the try (if allowed) would have been after time had already expired, so the game would have ended with England still two points behind.