Until relatively recently in bicycle history timeline, nobody chose what seat tube bore to use. They got a tube and used it (hopefully after checking that a shop seatpost fit okay). Even today, I think most people either do that or buy a pre-made sleeve that they weld in. Generally at that point there is enough distortion it needs to be touched up with a reamer a little. You want a sliding fit, so not too tight. Everyone hates it when the seatpost takes effort to get in the frame. It seems a bit surprising that someone would ream larger than a sliding fit.
But when I look up sliding fit, it seems tighter than what is used by the bike industry.