It sounds like sedum to me too. There are dozens of varieties and many look very different, so do a Google picture search for sedum and you may find them.

I'm thinking they could have been portulaca, but they shouldn't have flowered well with that little sun. They do come in all shades. Delosperma is another one- it's succulent, comes in lots of shades, but it wouldn't have many flowers in the shade at all. Million bells look just like mini petunias, but their leaves aren't succulent. I've only seen them in more rich colors, though so i don't know that it was the one.

For your spruce up, though- you could use sedum- there are a couple kinds that will do well in the shade of a tree. I don't think i've ever seen a sedum that had flowers like a petunia so that's why i' m a little doubtful that's what it was, but you could def use that instead. Good thing is most are perennial, so the new folks wouldn't have to replant yr after yr.

Delosperma 'Oberg' will bloom in part shade (as long as they have good drainage), and has pink or white flowers, but they look like daisies, not petunias.

Perhaps Begonias.

Here is a link that might be useful: