Grimma - if you are an atheist - then you put faith in your belief that religion and the very notion of god/s is man made - you don't know this, you can't know it, you can just believe it.
A lot of other put their faith in the fact that it's not, and really hope they've picked the right one.
While yoga might be not seen as a 'religious thing' for most people who do it, it is - it's part of another religion.
While it might be nice for the Church to be welcoming to other religions using their buildings, it's not that surprising they don't. Particularly if they weren't approached on the understanding it would be run as a religious meeting.
And as said up thread, a lot of church halls have conditions on their use that were put on the by the person originally donating them.