This is the problem of Hudson Rock making conjecture or trying to be authoritative when tbey don't know the process.
One SE is working on many accounts. Snowflake SEs don't build within the client environment typically. They set up a demo account like you or I do with the $400 in credits. SEs are constantly starting these. Why? They expire after the fact. The SE builds in the created demo account and shows the client. After 30 days Snowflake locks the account (no credit card) and subsequently drops the demo instance and data.
For an SE to do the work the customer can do one or more of the following: The customer's SF instance shares data to that demo instance created by the SE AND/OR the customer has given access to that Snowflake SE through SSO.
Either way, this is more of orgs not being restrictive in their security posture. There is nothing novel about this exploit other than they found an SE who was working very hard and clients who had not properly scoped the security permissions of an employee/contractoe/guest.