This is interesting for future reference so I hope the OP comes back to confirm. In theory, if the 7 year date has passed already, the OP already meets the requirements for PR which will be confirmed when they interview so the short period as a "visitor" will have effectively become moot as the PR will be dated from the application/7-year anniversary date. You just need to do the visa run to keep the computer happy I guess and maybe ImmD think this is the easiest way to handle it.
Alternatively, also in theory, if the 27th is the 7 year anniversary then being a visitor on 28th should be problematic as you really should have a valid visa when you apply (which can only be dated after the 7 years, even if you submit early).
Of course, it could be that the officer that answered looked at the information and thought it was ok and there is a little more leniency with this being a divorced dependant visa. (My son was born in HK but did his first 9 months as a visitor due to travel and passport timings and that was not a problem as far as ImmD was concerned as his own PR was granted for his 7th birthday).
It could of course be the answer was wrong (maybe it wasn't an officer), so I'd get it in writing first. I suggest going to ImmD on 26 or 27, get written confirmation before you leave to be safe.
ImmD do make the odd computer mistake, my daughter was flagged by the airport immigration computer as an overstayer despite her being PR for 2 years and having been in and out of the airport 4 times during that time. (I guess officers saw it but didn't bother to fix it).