I think it's just part of the twisted pretzel doctrine. They form a big dough wad of scriptures, then twist it and turn it till it fits.
They teach that everybody from Pentecost on till 1935 are of the 144,000 anointed priest class and will go to heaven to rule with
Christ Jesus as kingly priests. Therefore, when he instituted the "evening meal", it was for this priestly class only. Later, he said
he had sheep which were not of this fold and JWs connect that to the scripture that talks about a great crowd in Revelation. Then they fold that back
over on top of everything else, add a dash and a splash of extra reasoning, and voila!! .....a Big Twisted Pretzel of Doctrine....JW style.