Anyone else find it interesting that he wasn't wearing a knee brace, even a sleeve, while lifting? Could mean nothing and I don't want to start speculating, but it's a positive sign.
Knee braces are typically not prescribed or recommend for an ACL reconstruction. Knee braces are used to limit movement post surgery. for an ACL, you want that knee to move and things like a CPM machine can be used.
I'm not sure when he had surgery but what this could mean is he only had an ACL repair and not additional problems on the knee, but it really does depend on the timeframe because a brace is only used for 5 or 6 weeks max.
Edit: looking at the picture and seeing the scar on his left knee, that scar looks more like a hamstring graft or even a meniscus repair along with the ACL repair.