I think BMO is likely acting for a client that purchased shares  in the last offering.

Given there has been only one large seller over the past few days, and a variety of buyers, with the share price trending higher, it is not very likely that the selling is due  to one investor having expectations of negative news.

I think someone bought the new issue and is rebalancing their portfolio by selling shares they already had. A good trade for them, and helpful to Poet as well.