eyeslice:
In most instances where the NWT uses Jehovah in the NT it is a passage or expression from the OT where the tetragammaton does appear. In some cases it is quite clear-cut because it says "as it is written" or something to that effect. However, that is not the case in the example you give and so a consideration of the whole passage may be helpful.
14:3,4 "Let the one eating not look down on the one not eating, and let the one not eating not judge the one eating, for God has welcomed that one. Who are you to judge the house servant of another? To his own master he stands or falls. Indeed, he will be made to stand, for Jehovah [kyrios] can make him stand."
14:6 "He who observes the day observes it to Jehovah [kyrio]. Also, he who eats, eats to Jehovah [kyrio], for he gives thanks to God; and he who does not eat does not eat to Jehovah [kyrio], and yet gives thanks to God."
It is talking about not judging on the matter of food and drink. As you can see from vss 3-6 below, the context is that we shouldn't judge because God has welcomed such a one (whatever he eats). It is reasonable that kyrios in verse 8 also refers to God. However, I must agree that there is some ambiguity in this passage.
Earnest