Remember the top line, where they talked about this being a model of left tail risk (for investors).
They are predicting specifically that there is reasonable odds of a case where the stimulus is underbaked and too late, causing significant deflation, and a large number of past claims on future economic activity do not survive the restructure, and so every actor taking interest rate risk is at risk of getting blown out by deflation, or taking huge nominal losses from a default due to their counterparties getting blown out by deflation.
Remember the top line, where they talked about this being a model of left tail risk (for investors).
They are predicting specifically that there is reasonable odds of a case where the stimulus is underbaked and too late, causing significant deflation, and a large number of past claims on future economic activity do not survive the restructure, and so every actor taking interest rate risk is at risk of getting blown out by deflation, or taking huge nominal losses from a default due to their counterparties getting blown out by deflation.