HI,
If added through sap.
Check for the ULOG in the transport directory
sidadm 20130921122803 RFC: tp ADDTOBUFFER SIDKXXXX SID clientXXX pf=/usr/sap/trans/bin/TP_DOMAIN_SID.PFL -Dtransdir=/usr/sap/trans (pid=XXXX)
Search for the SLOG for that particular transport no related to the time 20130921122807.
In the Slog you will be able to see how it added via TMSADM or SID that imported it and the request got added as it was forwarded due to the configuration of the transport .
Please also check the transport route what system is before that system whose buffer you are checking.
Was that transport imported in the earlier system and the request was forwarded to the system next to it.
Try to check if up can find the pid=XXXX in the workprocess or SM59 trace.
Thanks
Rishi Abrol