Are you sure it was in USB mode? HM01 is almost always in AM, but of course there are sometimes mistakes.
Going to go over some basics here, if you already know this just ignore what I type.
When receiving a station you should always try other modes to see if it is really in the mode you think it is. It is possible to receive some modes in "other" than the mode they are transmitted in.
A station that is transmitted in AM can be received equally well in AM, USB, and LSB.
A station transmitted in USB will only be clearly heard in USB, and the same for a station in LSB, it will only be clear in LSB.
A station that is transmitted in SSB (either USB or LSB) plus carrier will be received in that SSB or in AM, but will not be received in the opposite sideband mode.
CW can be interesting, depending on your exact radio. CW can be received equally well in CW, USB, or LSB modes, but will indicate incorrect frequencies in USB and LSB mode, or if you are not tuned to the exact pitch in CW mode. The key here is that with CW signals your freq might be off by quite a bit, so if someone else reports it on another freq keep that in mind. Or if you are looking at freq lists keep it in mind. If you are receiving CW in SSB mode (either LSB or USB) consider that the actual freq might be +/- 2 kHz.
Hope that helps.
T!