I originally planned for all the other incarnations to be flying around in their respective versions of the TARDIS (or at least 10 and the war doctor) but then I don’t know, the idea of the Doctor and Clara running in to Harry and Ron during that part in TDoTD came to mind and I couldn’t help myself.
I feel like Clara would just be kind of speechless because suddenly she’s finding out that Harry and Ron are apparently not fictional.
Harry, still being a wizarding noob at this stage, wouldn’t actually realise that a man semi-falling out of a flying police box isn’t a normal thing to see in the wizarding world (which is easy to understand seeing as it isn’t exactly uncommon for wizards to have unorthodox flying vehicles and bigger interiors vs exteriors) and would be all excited and stuff.
Ron is the complete opposite of Harry as he knows this isn’t normal and is general scared by the fact this random guy seems so calm when he’s dangling upside down and from this high in the air.
And finally, The Doctor is just his normal, happy-go-lucky self, completely not bothered by the entire situation and just thinking “good old J.K.”