So, quick education moment.

Broadly speaking (that was a grass pun, we'll get there in a second), there's two types of grasses. There's broad leafs (think dandelions), and grass leaf (think grass).

Glyphosate kills grass and does not hurt broad leafs like dandelions. 2,4-D kills broadleafs and does not touch grass. That's why its safe to spray for dandelions in your yard, because it'll remove dandelions, clover, and other broadleafs without hurting your grass.

One of my first questions way up at the top of this thread is what actually happened to the lawn? Because if all the grass is still alive, but the dandelions are not, then glyphosate was not applied to the lawn. A broadleaf killer such as 2,4-D was likely used instead.