Is there any truth in this or can PV be connected first to a MEN switchboard or non MEN SWITCHBOARD (DB)?
We do not connect PV (photovoltaic generation) - which is d.c. - to any type of a.c switchboard.
What we connect at the switchboard is the output of one or more inverters, which are a form of electricity converter, and not a form of generation.
That may seem pedantic but the distinction is important.
The next thing we need to be pedantic about is whether this is to be an alternative supply or a supplementary supply.
As an alternative supply; the source can be connected to an installation at almost any switchboard.
There is no restriction in Wiring Rules that it must be an MEN swbd.
latest edition (2017?) of "301
Most "PV" is arranged as supplementary supply, rather than alternative supply.
Because it's intended to operate in parallel with the normal supply (generally via mains from a distribution network); additional rules apply.
Wiring Rules still permit connection at a DB, with some additional requirements around dealing with risk of back-feeding from the "input" swbd to one that would be "upstream" WRT the normal supply.
However the networks, and more importantly the energy retailers, insist on additional requirements; largely related to wanting to separately measure energy in and energy out (because different tariffs apply). Which have the effect of forcing these supplementary supplies to be connected at MSB. Even if the current agreement allows for simple "nett import" pricing, they want the ability to separately measure energy in & out.
So yes, there is a rule; but it isn't part of regulatory requirements; just the commercial contracts between a "prosumer" ( person who both produces & consumes energy) and the network retailer entities they are dealing with.
I don't think the location of inverter connection would matter as long as the meter is at the main switchboard so not sure why they would care.