I think the incident occurred literally a second or two before the stalls opened so no time to take him out, etc.
I think they’re on a tricky path here. Whose judgement was it that it materially affected his chance? The stewards presumably but it is at best a subjective assessment and done with hindsight after a poor run.
The horse was clearly a ‘runner’. He got a bad start of his own making but clearly took part.
If we’re declaring non runners on the back of every stalls incident with stewards judging whether or not the incident materially affected the outcome to ‘protect punters’ we’re on a path which will lead to more issues and disgruntled customers of the sport than would have been the case if they’d left things alone.
Should only be a non runner if the fault was stalls equipment related (e.g. gate opens late).