2) As of Supplement II: Blackmoor (1975), the monk was presented as a sub-class of cleric, so this was the logical presumption for where it would be classed in AD&D. Gygax apparently decided to make it a de facto subclass of thief when doing the PHB (thief for saves and attack matrix), then partly walked that back in the 1e DMG (moved to cleric for attack matrix).

As for the "also interesting" thing, let me quote the original three booklets, Men & Magic, p.8 at you:

Obviously, Gygax changed his mind on this (the 1e DMG, p.21, says effectively the opposite), but for "supported from the game's early days", well, it's hard to beat that.