OP, please keep in mind that you are the parent of one (1) six-month-old -- jolly, friendly, stationary, easily distracted, capable of being amused by nothing more than a spatula and likely taking 2-3 solid naps a day. You are solely responsible for this single child's daytime entertainment and well-being two days out of seven.
You went to go visit friends whose kids are less than two years apart, and whose mom is home with them all day, every day. Counting pregnancy, the mom likely hasn't had a full night's sleep in over three years. Or a restful daytime nap, either -- that whole "sleep when the baby sleeps" goes out the window when there's an older child marauding. When you noticed the older kid parked in front of the TV (probably so that the parents could deal with the baby or the household) did you offer to play Candyland or build a fort? When you noticed the younger one strapped in front of the idiot box (so that the older kid could have some attention, or so dinner could be made), did you offer to hold the baby, or take her for a walk?
In other words, did you at any point offer to help your friend by taking one or more children off her hands for an hour or two, or did you just sit in judgement while "Dora" scrolled by for the third time that day?
I would recommend trying on your best friend's shoes for a bit before you get too smug. Chances are they're going to feel just as uncomfortable on you as they do on her.