As others have alluded to, Chorus places no restriction on what grade of service can be connected at any particular property. There are some RSPs out there who routinely connect residential grade plans at commercial addresses for business customers, then the RSP puts their own business service wrap over the top. There is nothing wrong with this*.
In the OP's case I suspect it is Spark who have a specific business rule against it, most likely because there are other LFCs who actively prevent consumer connection types at business premises - so therefore it's easier for Spark to apply that more restrictive rule across the board to avoid any confusion.
*Where it can get tricky is in UFB1 areas, where a standard install distance allowance for a residential premise is 200 metres - whereas for a business premise it's only 15 metres. I have seen examples where a customer with a building 15+ metres from the boundary who is clearly a running a business from that building tries to connect a consumer grade service simply to try and avoid paying the non standard installation charge that would otherwise apply. They don't generally end up being successful.
The views expressed by me are not necessarily those of my employer Chorus NZ Ltd
I had a similar issue once with a customer (Motel) going back quite a few years who wanted to offer unlimited wifi to the guests and Netflix on all the in-room TV's, they couldn't because of the ISP imposed data caps on their "business" connection, they were unable to order a residential connection at the Motel. I told them they should talk to one of the neighbours, possibly run cat5e across or a small ubiquiti link as there was a block of flats less than 50m away over the fence.