Point of information, Mr Speaker...
According to my less-than-well-thumbed copy of Erskine May, there is a strict order of questions to the Prime Minister laid out in the Order Paper for the day and Mr Speaker was simply following the protocol and calling those listed on that Order Paper.
It was not a Commons debate as such - it was Questions to the Prime Minister and most back-bench MPs have to wait weeks for a chance to ask a PMQ. Unfair to pre-empt!
https://commonsbusiness.parliament.uk/Document/86044/Html?subType=Standard#_idTextAnchor001