It was common to experience some coughing and spluttering from the engine during a go around in a 152 or 172n following a practise forced landing. It was even worse it the power wasn't cycled properly a couple of times or if the throttle was advanced too quickly. Not saying this is what happened, but I've had a couple of 'oh crap' moments down at Kagaru despite applying the correct engine handling and airmanship techniques.
Out on solo training exercises you often wonder what students actually get up to. Despite the best instruction, there's a good chance they will be so task focused and forget to cycle the engine. This could end up being a good case study if it ends up being the case.
Jaba, not debating your comment, but why would a degree of fouling not be a potential issue? Given the conditions around SEQ this week, carby icing could easily be a likely problem though.