The FH-HG20 hub is definitely a Shimano hub, yes. I like their part number syntax...the first two letters before the dash signify the parts family. FH = Free Hub. RD = Rear Derailleur. Etc. The alphanumeric after the dash usually indicates the "line" or "group" of the parts (although the syntax on the right side of the dash is definitely looser). They used to be more consistent (like RD-MC31 or FH-HG20), but this has grown over time (to numbers like FD-M310 and RD-M4000, etc.).