I don't recall it ever saying to much about Magus/Magil in RD. We know from the CT ending that Magus was searching for something, even if he didn't know what it was.

There is an undisclosed amount of time between when Magus landed, and when the events at Viper manner began.

I say it's possible that in that time frame, either he managed to regain some of his memories, or he's simply drawn to Kid, unsure of why, but feeling it has to do with what he is searching for.

It seems more likely to me, if only because the CT bonus ending in the DS version strongly hints at that Magus's involvment in future events, something that just doesn't happen in Cross, but does happen in Radical Dreamers.