The Yellow Book of Lecan is a late medieval Irish manuscript; this verse, however, is much eariler. (Most Old Irish verse is transmitted in manuscripts that postdate at least some of their contents by centuries.) The latin title here is younger than the verse and might be contemporary with the compilation and copying of the book of Lecan (because titles tend to be fluid.) The Irish here looks like a fragment of a poem, or perhaps Roscada, embedded in a longer text; and the fragment was, as keberoxu explained, removed from its context.