"For those visiting what Im about to say in this talk I cannot back up or explain, so ask your teacher."
For a DO to be that honest that he can't explain 1914, 1919 (and maybe, I wonder, if he would include 'overlapping generations' also?) is being way too 'honest' for the GB to accept. (Unless, he later qualifies that he couldn't 'explain' only due to the 'time factor' required for his talk?) Anyway, for so many JWs there to respond so favorably to him, indicates that they too can't or are not comfortable with anyway for them to explain. The brothers and sisters would find that very relieving to themselves, that a DO can't explain it either.
Also, the "ask your teacher," is this his clue to any Bible Studies, to ask the one studying with them, a clue that they would no doubt find very difficult for them and perk up questioning minds.