That was then but this is now. The decision is to start the 5g network now and neither Nokia, Ericsson (or any other system level supplier) has products that compete with Huawei in the view of UK customers. The proposal is to limit the Huawei contribution to 35% so there is nothing to stop a competitive system supplier catching Huawei up and supplying up to 65% of the UK need (or even supplanting them).
5G is an international standard with full interface standards that establish interoperability between different equipment manufacturers. Telecomms is no different to any other industry in terms of such requirements, and in general terms, if there are interface issues, then reference to the absolute interface levels would identify which item(s) is(are) at fault. On a large system deployment, qualification and acceptance of the system would form an integral part of the contract. It's the same in far more important sectors such as avionics, which has absolute requirements to operate effectively in a degraded environment and in fail-safe modes. The most vulnerable interface in a mobile network is that between base stations and subscribers' devices. Those devices are examples of consumer electronics produced in a competitive market, hence the need for an effective interface specification. So by your reckoning, everybody should have either a Nokia or an Ericsson*1 mobile, unless of course the network has both manufacturers infrastructure elements*2, then you are stuffed. Apple might as well pack up and go away as nobody has an Apple equipped network.
No, that is a fallacious pseudo-technical argument presented as another excuse for avoiding Huawei, (who also make some good phones had you not noticed).
*1 Ericsson have virtually exited the handset market in the last 10 years so that could be difficult
*2 Some of the UK providers already use Huawei kit, Vodaphone for instance uses it in the UK, as well as Germany, Italy, South Korea, Russia to name a few. The list of those planning to include Huawei is far longer, and with the UK and Germany's announcements, that looks like Huawei will be regarded as a viable supplier.