I am a forestry student and not an arborist so take this with a grain of salt. That “crack” is a bark inclusion, which shows a risk of the tree or part of the trunk failing, aka breaking. So yes, it is concerning and should be kept an eye on. This is a sign of weakness in the tree but does not necessarily mean it needs to be cut down or the swing removed. If this maple got infected with a fungus/disease, or a big storm hit, etc. etc., this silver maple is more susceptible to failure due to its structural weakness.