That does look like frost damage on the new leaves; it may be that its new situation is a bit colder than where it was before, so I'd move it back to where it was and switch it into the less sunny area later on, when the weather warms up. It is quite early for a Hydrangea to be leafing out, April is the more usual time in cool northern climes, but when they ...
Based on the rounded edges of the eaten spots, it appears that you have slug issues. The rounded edges of the eaten areas are typical of slug damage - because slugs don't have teeth they kind of suck the leaf into their mouths. Here's an example of another slug-eaten leaf.
It looks like rust, which is a type of fungus.
There are many species of rust but this could be common rust - Phragmidium spp.
You should remove these leaves if you suspect it is rust to avoid further contamination.
Tomato plants don't like their leaves to get wet so you should water the soil not the leaves.
Looks like you are growing indoor under led ...