>Infectiousness may peak before symptom onset (7). Viral loads appear to be similar between asymptomatic and symptomatic patients (8), although the implications for infectiousness are unclear. People experiencing symptoms may self-isolate or seek medical care, but those with no or mild symptoms may continue to circulate in the community. Because of this, those without severe symptoms have the potential to be “superspreaders” and may have an outsized influence on maintaining the epidemic.
Source: https://science.sciencemag.org/content/370/6515/406
While it's not confirmed they are more infectious, they walk among the community without being aware, therefore more prone for spreading.