It doesn't matter too much really, it's just that mold likes stagnant, moist conditions, so if there is enough moisture in the container for a long time, it can condense a little and mold can develope over time. That's why I just like to leave my seeds in a paper envelope in the fridge, so there won't be any water condensing and moisture getting onto the seeds. (And drosera seeds don't usually have to be stratified
)
Now having a sealed container might be a good thing if there wasn't any chance moisture would be in there. For example, ig you used silica gel packets in a sealed container with the seeds, you could have the seeds last for a longer time maybe, since then there would be very little moisture within the container.