The only one I'd mildly worry about here (or perhaps even notice) is the man struggling with the fork. But as you were in a cafe where everyone had a knife, he probably had (or could have had) one too. Maybe it was missed or he dropped it on the floor and didn't ask for another or he didn't think to take one if cutlery was self-service. He may have dexterity issues in general and while fork alone is awkward, it could be what works best for him.
Otherwise, I think the US "traditional" way makes a lot of sense (if you substitute right and left for dominant and secondary):
Place settings still have the fork on the left and the knife on the right. If you (right-handed) sit down to steak, mashed potatoes, peas, and salad, you have the knife in your dominant hand as it will be cutting into the meat and separating a bite-sized chunk, while the fork only has to hold down the steak while you cut and then guide the portion to your mouth.
If you want a bit of salad, you put the knife down and switch the fork to your right hand to spear that. Then you may want to scoop some potatoes and peas with your fork, and you pick up the knife in your left hand as a guide; the fork is still doing the hard work. Switch back to knife in right and fork in left to cut more steak.
Two possibly relevant things here are (1) that it's pretty acceptable in the US to cut up the whole steak at the beginning and then put the knife down unless you need it to guide food (weaker hand is fine for this) or to butter bread, etc. and (2) that for a while knives just simply weren't available in certain areas (the Wild, Wild West!) because of the prevalence of gunfights.
For your friend who doesn't know how to set the table, I think there are lots of resources online, or via a library or bookshop if she's not on line, that would sort this out quickly!