The primary difference between Crassula and Portulacaria is growth habit, and it only becomes evident over time. Crassula supports itself, whereas Portulacaria produces growth that may droop and may need support to keep it upright as a houseplant, although sometimes, its growth gives it a rather 'spiky' and untidily upright overall appearance. The stems on Portulacaria are also often noticeably dark, with a purplish red colour, seen in one of the images here http://worldofsucculents.com/portulacaria-afra-elephant-bush-dwarf-jade-small-leaf-jade-porkbush/. The tendency for new growth to droop or trail here https://www.gardeningknowhow.com/ornamental/cacti-succulents/portulacaria/growing-elephant-bush.htm. It's certainly possible that the plant in the original question is Portulacaria rather than Crassula; if any new growth produced tends to trail, or has obvious purplish stems, then it's Portulacaria.
Either way, care instructions as a houseplant are similar. Portulacaria is less common as a houseplant, and is so similar it's sometimes given the common name of 'mini jade plant' or dwarf jade.
The flowers are different on each plant, but Crassula kept as a houseplant doesn't often flower - not sure how likely Portulacaria is to flower if kept in a similar fashion.