Hi @roberto,
Thanks for flagging this, and apologies for the friction during the security review. To answer directly, the "SharePoint Subsite" field on the connection screen does not act as a hard permission boundary. It's a default that tells our SharePoint tools which site to target when the per-call site_name parameter is left blank. The OAuth token issued by Microsoft still carries whatever tenant-level access the consenting user has, which is why your read tools can reach content outside the subsite you entered.
Lmk if this helps!