As an Indian national, you are allowed entry visa free to visit for a period not exceeding 14 days. However, pre-arrival registration is required, as you note.
The Immigration Department states that nationals who are allowed to enter Hong Kong without a visa may do so for tourism or business-related purposes, the latter limited to:
[C]oncluding contracts or submitting tenders, examining or supervising the installation/packaging of goods or equipment, participating in exhibitions or trade fairs (except selling goods or supplying services direct to the general public, or constructing exhibition booths), settling compensation or other civil proceedings, participating in product orientation, and attending short-term seminars or other business meetings.
Your 4-day training would appear to come under participation in product orientation, short-term seminar or other business meeting.
Indian nationals are required to apply for and successfully complete pre-arrival registration (PAR) online before they can visit the HKSAR visa free. Please click here for details of PAR.