When Hong Long and the man in the azure robe had been talking, they had lowered their voices so that Lin Fan couldn't hear what they were saying. Of course, he could hear a few things when they raised their voices, but beyond that, he didn't really hear the bulk of their conversation.
It wasn't that Lin Fan wasn't interested, it was just that he trusted Hong Long since they had also spent quite a bit of time together.
Along with Momonga, Hong Long had also taught him quite a bit since they were both body cultivators. As well, since Hong Long was a Dragon Race Expert, he had also been teaching Xiao Feng quite a bit.
So when Hong Long and the man in the azure robe came over, Lin Fan didn't put his guard up because of his trust in Hong Long. However, it wasn't just his trust in Hong Long that caused him to make this decision. It was also the fact that the man in the azure robe didn't have any hostility at all.