Im a XGSPON customer, and there was no additional cabinets installed in my area, and there is no requirement to do so. The serving cabinet for XGSPON can be miles away in another village as light can travel over greater distances than copper. Also, as they are using Openreach's ducts they would need to potentially dig up the road and modify openreach's inground ducting to route to a new cabinet, and i'm not quite sure thats permitted on the PIA service from Openreach, so i highly doubt those cabinets are anything to do with Nexfibre.
Look at the top of the Openreach telegraph poles, if you see a fairly large black box thats been recently installed, that is a Nexfibre CBT. (A fibre connection point). - All Nexfibre's work (AFAIK) are delivered using PIA scheme. PIA (Physical Infrastructure Access) is a service provided by Openreach where other Altnet's are able to utilise BT's existing inground ducting, and poles to run their fibre to homes.
The only real way of telling if Nexfibre are in your area is to look on https://bidb.uk under 'roadwork providers' you will see Nexfibre, and then check on the telegraph poles for the black CBT, or yellow identification tags on the fibre cables going up the telegraph poles, it will say something along the lines of 'Property of Virgin Media'.
I have a feeling you may be in an area where Virgin themself are upgrading from HFC, and you may find you will get put onto RFoG which is marginally better than HFC. - Once you have RFoG you can easily be switched to XGSPON or GPON depending on which service VM chose to send over the fibre to your property.
Hope some of this info helps.