Dragon was present in Loguetown in Chapter 100. Why? I think it is one of 2 reasons. He came for resources. They got resources from Zoro‘s village in the East Blue. So it’s not far fetched to say he could’ve gotten resources from Loguetown as well. And reason 2 is of course, he was there for Luffy. He somehow, someway came to know that Luffy would be in Loguetown, and he came to visit him. Here’s what Dragon had to say to Luffy, ”A pirate? That’s fine too“.
Too? Did Dragon have any other plan in mind for Luffy? Did he come there to recruit him into the Revolutionary Army? Did he have any other motives? We don’t know.
Dragon has constantly been in action in the shadows. The reason he gained such infamy throughout the world, was his liberation of countries under the World Government. Dragon has constantly been converting people to stand against the World Government throughout the world.
Dragon is seen to be looking at the East every time he sets sail sorta drawn by the East Blue. But he doesn’t like anyone prying into his past.
WHY I THINK HE’S NOT A MARINE
Here’s the deal. I have only a rather really simple reason. Let’s say Dragon was a Marine, and he quit because of how corrupt the Government was. Garp has to know this. He has to know the reason Dragon quit. Even after his son quit the Marines because of the corruption, why would he force Luffy and Ace to the same path? Why would he try to do something that pissed his son off, to his grandson? It doesn’t add up.
Throughout the entirety of the Marineford war, Akainu doesn’t call Ace, Roger’s son. But he constantly keeps calling Luffy, Dragon’s son. In such a way that it almost seemed like he hated Dragon on a personal level. He wanted to kill Luffy not just because he was a strong pirate worth 300 million, but because he was Dragon’ son.