I think someone on Reformed Forum said that the superscriptions (the bolded titled lines in most Psalms in the modern translations) were not originally in the scripture. Was it Jim Cassidy? I can't remember.
However, most sources point their existence to the earliest manuscripts (i.e. Masada Psalms Scroll (MasPsa) from the late first century BC, Aleppo Codex (ca. AD 930), the Dead Sea Scrolls, etc).
I wonder, when those who said that it's not part of the original scripture, were they basing it on some obscure manuscripts or even worse, that because these superscriptions do not, according to their view, convey any spiritual meaning and thus not considered part of the INSPIRED Scripture.