The problem with the wt understanding is, that by watching for who is partaking you can (kind of) determine who Christ's brothers are, therefore limit your charitable works to that genre, and make it "spiritual" rather than real. The other problem is that who is really sealed to be of the 144 000 is only known to the angels, and even then only at Armageddon. so
what Jesus recorded words probably mean is, do good to all, because you never know who you are doing it to, you might hit the jackpot by doing it to one of God's sons. and
The "other"sheep could not possibly be the JWs because they know perfectly well (in their opinion) when they deliberately do a good thing (contributing) to the Leadership, the really anointed; so they would not ask that question.