I am sure he realizes that his kindness has added to my own collection of material. In the event that I do publish in the future I will cite Dr. Willker's generous kindness for having pointed this out to me. The following below also expands on this. I have analyzed this and found the first two possibilities a bit unfair to assign a scholar. I have concluded that Schubart must have been citing a work directly.
Every scholar cites sources.
Since no reference is given it necessitates none was necessary. When one cites the text of the author cited. This was my rationale. Based on this logical analysis it seems clear that Schubart's work suggests he knew of a Papias ms. Perhaps you'd like to offer your own opinion on this matter.