I think he needed 2 snookers (or more exactly 5 points worth).
There was a bit of confusion at the end as the score was 7-51 when Trump potted the red and went in-off. The Scoreboard credited Trump with the red but didn't add Ali Carter's 4 points.
So the scoreboard displayed 8-51 (43 behind with 43 left), but the actual score should have read 7-55 (48 difference).
I'm not sure if Trump knew what the score was but he certainly conceded too early! He should have given himself a moment to compose himself and 'digest' the state of play - but instead he petulantly threw the a ball up-and-down the table!