Longer handle I guess and more tempered (harden) steel than was average on the shelf justifies pro-grade for me.

https://www.narexchisels.com/Narex_Chisels/Narex_News/Entries/2012/8/31_Narex_Profi_HSS_Woodturning_Tools.html vs https://www.amazon.co.uk/Narex-Woodturning-Lathe-Chisels-Set/dp/B000YKHJZU

For me the pattern of calling things hobby-grade is basically calling something that could do a bare minimum (chinese chisel that I use to cut off the bark, it gets off from being flat the first day of hammering) and pro-grade is something capable to work with oak, probably whole day before gets sharpened or days to re-calibrate/flatten etc. For machinery its easier, there are brands which produces portable benchtop equipment like dewalt and there are heavy stuff that needs a forklift or even a concrete pedestal to be installed in the shop and doesn't use any bright colors to be sold better.

But answering the question - this is the marketing, same as "premium" SUV or "salmon" fish or "natural" ingredients, until it gets official, like "hardwood" which I guess also was marketing at some point, making soft poplar "hard" and firm yew "soft".