Hi! High amount of fibre rich food can also sometimes cause soft or loose stool. Other causes of loose stool can also be sudden change in food, stomach parasites, GIT infection etc. If its only one time occurence then you can give some bland food like boiled rice and chicken (slightly soupy) for 2-3 days.
If you observe any of the symptoms like vomiting, soft stool turned to loose stool, inappetence, I would recommend you to book a vet home visit or a vet video condultation.