Only slightly true. He was granted permission to buy up to 25% stake. Squeeze won't be felt until the buying is in motion and the float becomes non-existent. Also as part of the additional buying is the trickle up in price and the position of Ackman goes from black to red. THEN not only is the squeeze on but Ackman's hand will be forced! Bail or suffer the shareholder wrath/abandonment.
Ackman's entire premise requires action by the FTC. IF there is not a case being built now then a case won't be built and brought this year. BAD premise for a short. When Ackman's position goes red he will bail. SELF-IMPOSED squeeze.