Could aliens have discovered Earth from our radio signals?

Yes — in principle, but it would be very hard and is considered unlikely from ordinary radio and TV broadcasts alone.

Radio waves travel at the speed of light, so Earth’s earliest broadcasts have been leaving the planet for about a century. That means only relatively nearby stars have had time to receive them. But ordinary broadcasts spread out in all directions, so their strength drops rapidly with distance and they become extremely faint by the time they reach interstellar space.

A more plausible way an alien civilization might notice us would be through much stronger, more focused transmissions such as planetary radar or deliberate interstellar messages. Those would be far easier to detect than everyday leakage from radio, TV, or cell signals.

So the short answer is: possible in theory, but everyday radio signals probably would not make Earth easy to discover unless a nearby civilization had very sensitive equipment and happened to be looking in our direction.