That denial shouldn't be a big deal for Akira, seeing how just days ago he didn't even know these folks exist. So, even if he was told they are his relatives, he doesn't know them at all, forget about feeling kinship with them. So, basically, it would have all been up to them to make him feel welcome. If they had, perhaps over time he would have started to have positive feelings about them. The geezer pretty much destroyed that possibility, so they will remain as strangers. The geezer will reap what he sowed.
But then again, this series is what it is and Akira is a blistering idiot. It wouldn't surprise me if he dropped onto his knees to beg for the geezer to forgive Carl and accept Akira as his grandson.