Don't know where you are.
Were they seedlings or young plants?

"tender" seedlings are those that grow in the heat, like tomatoes, squash, basil, etc.
they don't like below 35 degrees with no protection at night.

rather than worry about it, just toss a light covering over the pots until you are sure of weather.

Cool weather plants like lettuce and broccoli can handle 40 degrees at night with no protection unless they are very very young.

if they are in the area where frost hits them....I find that areas close to the house do not get hit when the open field is covered in white frost. You can cover the plants so the frost doesn't hit them, or watering down the plants will protect them. I used the wetting down plants technique all the time in Houston, when frost was expected. This will not work for a very heavy frost.

I've had perennials pop up and literally freeze solid and still survive. At the moment I have nothing outside as we are still getting hard freezes every other night or so. Usually if annuals suffer frost damage it's pretty obvious within hours. They start drooping and discoloring.

If it was just a light frost, it may have been warm enough near the house to protect them.

covering them up if they predict ANY frost - no matter how warm it is.

I just started my seeds this week because it can frost right into mid May. And even once the frost danger is gone, it's so cool the peppers and tomatoes just stall.