what those people said is wrong.
The ranking system is based on the chess ELO rating system. that basically means, everyone started at 1600 and the better player you beat the more your ELO goes up (rank)
so say you 1601.53 and you beat someone with a 1645.12 your ELO will go up a lot more than beating a 1602.01
Your rank changed so much over night because it was updating all your wins, and everyone else's
rank is based on your ELO 1708.99 ELO will probably make you top 10 players. Don't rely on rank so much