Moon can simply mean unexplored feelings at it's core. It may be an "empty" card in this aspect... there is a first impression, but overlying that is a lot of foreign conclusions and feelings that need to be drawn outside the realm of "normal". They're not making a swift judgement yet as to how they feel because there still seems a lot of room for different conclusions to be drawn... they may even feel unsure of themselves and their ability to read others when this person is around. (causing anxiety for instance)
However, if beyond that point, it may also be someone "charmed" by this person in some sense--but not necessarily enough to give in to the call of the wild the more imaginative aspects of this card... they may not imagine anything elaborate. It may be that they can "see" the person being good for general adventures, mainly short-term excursions, as friend or not, say a dream date or trips to the "wild side", etc (think fantasy)... but there may be some notion that it may not work long-term if the question is romance-based. They may have already made this estimation and fully accept this... acting on their emotions (purely) would be a trip.
I'd say it depends on how "fresh" and instantiated the Moon card feels to you what it means. If it's well-entrenched, the person may have made some strong observations. If it's someone they hardly know, then it's more likely this this person feels "enigmatic" to them and that they themselves feel compelled to feel differently than they normally would when they are around. This doesn't mean romance, it just means the relationship (for now) is all about thinking outside the box... They may not fully understand each other, but they're perplexed by them -- which keeps things interesting...
With romance, I usually connect this card with high school romances (the often unrealistic "We're going to be married and have six kids!" even though we're all moving away kind), as Mystica7 put "They are so very in love, they suffer."... they don't think anyone else "gets it"... it is like a small world that only exists to them. Dream dates to amusement parks, trips to Vegas, eloping, etc, they can provoke similar feelings...
For a great deal of people people though, these mental excursions often prove to be too rich for the palate (it's not what our culture treats as "reasonable"). They don't open their mind easily, because often it's the "unknowns" that open them up to hurt, they were either told or taught never to be that vulnerable...they may have had these experiences, so they may feel skeptical of their own "take" on the situation. Though there's a voice in the back of their mind "not to over-think" the connection with the other person... maybe the other person is acting out quite a bit when they are around each other, leading the other person to draw what feels like "presumptuous" conclusions and the Moon card is signifying the amount of confusion (and anxiety) they are enduring, as this relationship is beyond the ordinary...
I would be cautious about things like people's emotional boundaries in these cases... Moon can be sometimes be a signal that another person's emotional buttons are being pushed and they're not exactly sure why and for what reason. On the other hand, they may feel this is the other person, that they are easily triggered emotionally in some way... they may be all over the place, at least relative to them, and this is "new territory" for them
Anyway this card often thrives in the "greys", so I would not look too hard for anything black and white and specific when it comes to it's definition. It can just as easily represent feelings that change from one minute to another... hot to cold... and back. So you may need to check later when the relationship is less "liquid"...
Edit: Added some things.