There is a sangraha rAmAyaNa written by Narayana Panditacharya, who also wrote the maNimanjari and sumadhva vijaya. I have not seen the work and so cannot comment on whether it describes Anjaneya as an avatAra of vinAyaka. I would be very surprised if it does, given the unique mAdhva emphasis on the connection with vAyu, which links hanumAn, bhIma and AnandatIrtha in their hagiography.
That apart, this particular composition is spurious. To my mind, it is not by tyAgarAja and it is not attested within the main lines of the composer's Sishya paramparA. It seems that whoever wrote this could not make up their minds between attributing it to tyAgarAja and muttusvAmi dIkshita, for there is the guruguha mudra in it as well. Even varaSikhivAhana, a genuine composition of tyAgarAja's in the rAga supradIpam, does not have the word guruguha in it.
It is very likely that the term AnjaneyAvatAra is a forced construction, meant to meet the constraints of dvvitIyAkshara prAsa in the caraNa sAhityam. There are a lot of such compositions floating around, attributed to one of the great composers of karNATaka sangIta, which are teasingly described within the musician community as "factory output." Some of these questionable compositions do have good musical and lyrical content and so even the better quality musicians continue to render them, knowing full well that they are of questionable origin. Most other such compositions continue only in the printed medium and are rarely, if ever, sung on stage. Even SyAmA SAstrI, whose musical style is extremely difficult to imitate, has not been spared by middling composers who want to ensure a longer performance life for their creations. There is a small set of highly doubtful compositions with the SyAmakRshNa mudra known today, which lack the grand structure that is his musical signature.
Best regards,
Vidyasankar