Not unusual. The spores or mycelium will have been in the compost and like the tomato plants you have given the fungus the right conditions in which to grow.
If they bother you, pick them out.

I agree with Owd. But dont eat them as no idea what type they are.

Compost often has fungal spores in it as fungi are one of the active organisms that cause decomposition.

Thanks

Those are rather nice aren 't they? Just enjoy them, they won't live long/

I was thinking the same, Stera.