Why are economists concerned about treasury purchases in the Cayman Islands?

• https://www.federalreserve.gov/econres/notes/feds-notes/the-cross-border-trail-of-the-treasury-basis-trade-20251015.html

"As shown in Figure 5, between January 2022 and December 2024, a time when the Federal Reserve was reducing the size of its balance sheet by allowing maturing Treasuries to roll off from its portfolio, Cayman Islands hedge funds purchased, on net, $1.2 trillion of Treasury securities. Under the assumption that these purchases are comprised entirely of Treasury notes and bonds, they absorbed 37% of net issuance of notes and bonds, nearly the same amount as all other foreign investors combined."

Additionally, do these leveraged Treasury purchases have effects similar to yield curve control in terms of suppressing yields or stabilizing the long end?