From The last will and testament of Gen. George Washington (1800)...
... my intention being, that all accounts between them and me ... shall stand balanced.
Note that words like intention, meaning, reason, point all overlap in various contexts. And as this 1727 instance shows, point has been around with this reason, argument sense for a long time.
Presumably what OP finds "odd" is the word being, in a construction where the more obvious verb form would simply be is. To be fair, Robert Noggle at Central Michigan University also says "the reason being [some reason]" is somehow invalid (he certainly doesn't like it), and maybe there are others who feel the same. But I disagree - it seems like perfectly standard English to me.
Arguably in some contexts the present continuous "being" emphasises the ongoing nature of whatever is being referenced more than simple present "is". For example, "My point being that X" could imply some "insistent" sense of "My point continues to be / has always been that X".