Complete garbage, for several reasons including those already given by others.
Are you expecting the cabinet to be enabled for FTTC (VDSL2) or FTTP by the way? The way the two are delivered to the home are very different. But in both cases the service between you and the exchange is completely provided through Openreach, and they are legally forced by Ofcom to treat all ISPs the same in respect of making a connection available
On FTTC the fibre stops at the new cabinet and the circuit is from there to the phone cabinet and on the existing phone line to the house. On FTTP there isn't a new cabinet and the fibre comes all the way from the exchange to the house.
I'll assume it is FTTC you will be getting.
At the new FTTC cabinet there is a DSLAM which is similar to the exchange equipment that handles your broadband now. Connected to that are several "line cards", each with several connectors. One connector per FTTC customer connected to the cabinet.
Those DSLAMs can have multiple 1Gbps fibres, (I think some might have multiple 10Gbps ones these days), back to the fibre exchange head-end. Don't forget that as soon as the customer is a hundred metres or so away the speeds they can connect at fall away from the maximum 80Mbps.
At 600 metres my connection is ~57Mpbs and for people further away it falls off rapidly. Bear in mind that someone who isn't streaming produces relatively little throughput on a consistent basis, and it is only the actual throughput that travels along the exchange <> cabinet fibre. Not the total of the connection speeds.
Barring a fault or problem of some kind which gets fixed, congestion between users and the exchange doesn't happen. At the exchange the ISP buys a 1Gb or 10GB connection to the Openreach fibre termination kit from its own backhaul. From thereon it's entirely up to the ISP how much capacity they provide - just like it is with ADSLx.
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 57825/13835kbps @ 600m. - BQM