No, you are not required to disclose ShortVids as the production source to your end clients. However, ShortVids is not responsible for maintaining that confidentiality on your behalf: if your own client discovers the production relationship through means outside ShortVids’ control (e.g., your own communications, invoicing, or team disclosures), that is not a ShortVids breach.
If you need a formal mutual confidentiality agreement covering how the relationship is referenced by both parties, request one from your Account Manager, this is available for agency/reseller accounts on request, not automatically.