The class could be as small as one candidate done by courtesy at another lodge, but I doubt that's the case here.
Or it could be several Brothers raised the same night, not necessarily all from the same lodge. Both of my Illinois lodges put out general invitations to there districts when doing degrees and often do several candidates in the same night. The obligation part gets done in parallel (maximum of 3 around the altar), the second section individual, the lectures in parallel. Three or four are common as a class for 1st or 2nd degrees. I've never seen more than 2 for a 3rd degree.
Or it could be a larger festival sponsored by the Grand Lodge.
In any of those cases I can imagine the lodge doing the degrees might have a different tradition on the certificate. My mother lodge gives out several mementos but not that certificate. I had to order mine directly from my Grand Lodge because I decided I wanted one in addition to my dues card.