Oh lord, this comes up about one or other of the contestants every year!

'Dance training' does not mean
ballroom and it's an entirely different specialty to any other kind of dancing (including what you might call 'dancing' on stage with a pop group).
I'm not sure you can call that
'dancing' anyway - it's
choreography! Doesn't mean a singer/actor can move any better in a dance off-stage than any of us normal punters can!
Choreography is something that takes place over a period of time concentrating on one or two particular set dances. If any of us were choreographed for that long,
we could probably perform passable 'routines' on stage whilst attempting to sing (the latter especially in my case!).
Doesn't mean we'd be able to enter 'Strictly' and be able to do a foxtrot/samba/cha cha/waltz etc etc etc!
Or that we'd been 'trained as dancers'. That's not what it means.
A lot of the celebs (actors etc) have been to stage school, but unless they specialised in dance - and I don't believe any of them have - then presumably, it was just a lesson in the curriculum which they had to attend whilst they got more rigorous training in singing/acting etc.
It's not something they would have been spending an enormous amount of concentration on if they already knew their path (acting/singing etc).
If they
had specialised in dance then they wouldn't be known as actors or singers or whatever. They would be actual - you know - dancers (either famous or chorus line)!
And that would have precluded them from taking part in 'SCD'.
Also, a lot of people have 'natural rhythm' - even with no 'training'/previous choreography whatsoever. Doesn't mean they've had previous experience. Just means they are naturally talented - and I always think it's a teeny bit unfair to try to detract from someone's natural ability by claiming they were taught it at an early age. Why can't we just accept that some people are just naturally gifted in certain areas? (Not that I'm saying you were doing that personally, dancingfan!)
They can't be good at everything - there's probably somewhere else where they're deficient (like maths, for example - my personal bugbear! Or remembering birthdays or ... you know!)