Last I interacted with toptal, the 'leetcode-style' UI was 'work on your own' as a filtering mechanism. I hit similar problems before, where the problem itself was - to my reading - ambiguous and confusing. And you just had a 30 minute timer ticking away - no way to ask a question of anyone at all.
In the example above, I was, indeed, talking out loud to someone and we had some clarification and discussion, but it was still more contrived (imo). Working with the first person with real SQL and a set of real life tasks (write a query for a report to give number of active employees in each area, etc) was far more straightforward vs "find non-repeating chars in a string". I can do the second one, but I wouldn't work by starting off fresh pairing with someone. I would start off a problem on my own, document/test/trial things, then if/when I needed to pair, I'd be able to walk through things in a more measured process. Give me 10-15 min on my own to digest the problem first before I talk to someone.
Even writing this, I can hear people say "but that's how the real world works! You have to jump in to unknown problems immediately pairing with someone, and just ... ask away for clarification..." But even then... it's not how I work well in contrived online tests. In a business setting, the team is likely all 'new' to at least some of the problem. In the 'exam' setting, I'm still 'pairing' with someone who knows it all, and the 'hrm...' and 'do you need help?' interjections every few keystrokes is just not conducive to real work (for me), nor is it how I would ever work in real life.
