Healthy relationships have a tendency to grow more slowly. A person with secure attachment tends not to instantaneously fall completely for a stranger and then immediately start treating them like the stranger is the love of their life. That’s a love bomb. It’s the way a young teenager expresses love for their crush.

On the other side of the coin, if you met a new person and they immediately started talking about how they were completely in love with you and showering you with attention and affection that didn’t have any real backing in a developed relationship, it might make you uncomfortable. Unless you are feeling very insecure, in which case this behavior might seem like a gift from the gods.

Over-all it’s the lack of boundaries or long-term plan to follow through that differentiates honeymoon phase from love bombing. The narcissistic person just wants the attention, even if only for a couple of weeks. It can leave the other person feeling used.

My impression is it's the 'one sidedness' of it. Where all of the sudden you're just inundated with lots of praise and love. Whereas a honeymoon phase its gradually increasing and two sided?