WHAT DOES EXTERNAL TRAFFIC MEAN?
Seconds, you got their attention by forwarding your card which could be resulting in viewing more of your cards which finally increase the spread of your cards (spread has high priority in challenges to get ranking, more important than number of votes).
All above summarized results in
You can also find more info about "external traffic" by joining SKB (sola knowledge base):
You find there a card, explaing all sola used words like:
Spread, channels, challenges, Reading, follow, prioritize, fraud check, sola rules and all others.