Ann: Issuance of Milestone Shares Under Vaxinia Acquisition, page-19

A voluntary escrow arrangement is a contractual agreement whereby the holder of securities agrees not to dispose of its securities, or rights or interests connected with the securities, for the duration of the arrangement.

In the announcement it is stating -
"If shareholder approval is obtained and the Milestone 1 Shares are issued, those shares will be subject to voluntary escrow for a period of 12 months."
He can't sell till out of escrow, so he will be wanting the SP to be as high as possible in 12 months time.