He wasn't 'demonstrating' or 'relying on' expertise. He was sounding as if he was an expert by not caveating it.
Non-sense on stilts. Sounding like he was an expert on what NS?
People do not assume someone is an expert when they voice an opinion, unless they caveat it. They just assume that they are expressing a non-expert opinion. Here are some examples:
Q - 'I think you met Jim yesterday - how was he?'
A - 'OK, but he's really struggling with his back at the moment'
Real people conclusion - person is expressing a non-expert opinion on how they found Jim.
NS conclusion - person is portraying themselves as an expert orthopaedic practitioner, unless they caveat that they aren't an expert in orthopaedics.
Q - 'How was the film you saw yesterday?'
A - 'Bit shit really - didn't enjoy it at all'
Real people conclusion - person is expressing a non-expert opinion that they didn't like a film.
NS conclusion - person is portraying themselves as a expert film critic, unless they caveat that they aren't an expert in films.
Q - 'What did you do last night?'
A - 'I went to that new restaurant on the High St - it was really good'
Real people conclusion - person is expressing a non-expert opinion on a restaurant.
NS conclusion - person is portraying themselves as an expert restaurant critic, unless they caveat that they aren't an expert on restaurants.
Q - 'What 'expertise' was Starmer demonstrating or relying on NS?'
A - 'He wasn't 'demonstrating' or 'relying on' expertise. He was sounding as if he was an expert by not caveating it. Politically that's the position he's ended up in hence he's already fallen foul of the Biden gaffes. Your political naivety is showing again.'
Real people conclusion - person is expressing a non-expert opinion on the Biden/Starmer situation.
NS conclusion - person is portraying themselves as an expert political commentator, unless they caveat that they aren't a political expert.
But trust me NS - no-one thinks you are an expert on politics even though you never caveat your opinions