devtrackers.gg
Well, in free roam you aren't technically in a team with the randoms, so presumably the only way to get shared medal experience in free roam is by manually grouping up. Could be that they meant, and/or in the context of the crit path where you can play completely solo, but teaming up (either with friends or through matchmaking) might be more rewarding.
Personally, I certainly hope there's no distinction. I vastly prefer in-game matchmaking over third-party systems, so I would hate to be disadvantaged - even if it's just slightly - because I'd rather use the actual in-game system over something else.
When you're in a group with others (you're automatically grouped with matchmade players in Strongholds and Missions), you share the XP gained from your Feats.
The only time you don't share XP is if you're by yourself in Freeplay (not in a pre-made Squad). The easiest way to look at it is... if you see them on the Victory Screen after the expedition is over, you're sharing XP with them. 😊
Edit: Also, just a note... the word "sharing" might be a bit confusing. You don't split XP as a group... you just get more. 😊