How did Hub and Garth know what happened?

Question

In the 2003 film Secondhand Lions, teenager Walter lives with his uncles Hub and Garth. During the summer he gets a pet lion, who later

has a heart attack while protecting Walter from his mother's abusive boyfriend Stan.

Attempting to make Walter feel better, the uncles state the following:

Hub: She died with her boots on, that's the main thing.

Garth: (pointing at Walter) Protecting her cub.

At the time, however, they were in the house and supposedly asleep. Walter's mother was watching for them, and the three ran out of the house after hearing Stan's screams.

How did Hub and Garth know the circumstances of the death, or even who Stan was?

Answer 1

The script makes this clearer.

Hub: Oh, he'll live, I was talking about the lion.

All see Walter's bruises, put two and two together.

HUB (Cont'd) What happened... did he do that?

Hub GROWLS and grabs Stan, but Garth stops him.

Unfortunately, this particular scene seems to have been reduced in editing (the italicised lines don't appear in my copy of the movie) however if you follow the action along you can see Duvall start to point towards Osment as if to start saying those lines just before Caine mentions taking Stan to the hospital. It's quick but it's there.

There are no "bruises" on Haley Osment as such but we can see a red mark where Stan slapped him while he had Walter pinned on the ground.

There's no indication that they knew who Stan was but what he was doing seems to have been obvious.