Uhhh, no mate. That's just bad math... and I can tell you that as someone who is terrible at math. Ironically you're trying to make a very simple problem overly complicated when in reality you're dealing with a flat multiplier which means you can just push the values up by the number of 0s in the multiplicative value. In this case, 9 0s in 1,000,000,000
0.0064 - 0
0.064 - 1
0.64 - 2
6.4 - 3
64 - 4
640 - 5
6,400 - 6
64,000 - 7
640,000 - 8
6,400,000 - 9
Or you could just, you know, plug it into any calculator lol, which is how I imagine most people in this thread initially got that value (Myself included, just googled "1 billion JPY to USD").
0.0064 x 1,000,000,000 = 6,400,000
As for the manga itself, its probably gonna suck and get dropped. Art is good but EVERYTHING in this chapter save exclusively the main character being absolutely stacked is extraordinarily generic. Though ironically, I find myself intrigued just because of that one element. I find myself curious how the author intends to make us care about an MC who is billionaire levels of rich... I mean, he's already kind of broken the suspension of disbelief here. Not only is the MC not an insufferable twat despite having grown up unfathomably rich and privileged, but we're supposed to believe a kid who can throw money around like that has trouble making friends? Sure, they may be superficial, but he's a student still for fuck's sake.
Either way, I'm willing to be surprised. I doubt I will be, but hey.