Being inside doesn’t necessarily mean that slugs or snails can’t get them. Some small slugs live in the soil/compost ... they could’ve hatched from eggs in garden compost or soil or even in bought in potting compost if it had been standing around in the garden for a while.
Also check out the rims and bases of your seed trays, modules etc ... they provide great winter hiding places for tiny molluscs and if they’ve been sitting in a garden shed or whatever before being used they could have residents you’ve not spotted.
It does look like mollusc damage to me.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
Posts
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.