The translation comes from Hans Lietzmann’s Das Muratorische Fragment und die Monarchianischen Prologue zu den Evangelien (Kleine Texte, i; Bonn, 1902; 2nd ed., Berlin, 1933) available here.
. . . at which nevertheless he was present, and so he placed
Lietzmann’s footnote reads,
The meaning may be that Mark arranged the material of his Gospel in the order indicated by Peter, who was participant in the events narrated.
But this is an assumption based on our canon. What if Mark was first? What I mean is this. Papais was hesitant of Mark because it only recorded Peter’s words, but Matthew as supposed to be an eyewitness. So, let us consider Matthew as the only who “was present” so he placed… events not in Mark “in his narrative.” This would, for a late second century canonizer, explain the differences and added detail to Matthew not found in Mark.