Taken at face value, the statement is implying that it is something to "consider", even though your traffic could be considered "safe" if it uses IPSec (or SSL). Perhaps the statement makes more sense when taken into context of the entire article:
- Connecting over the public internet: traffic can be intercepted over the public internet (and read if not encrypted).
- Connecting with a point-to-site connection: traffic can be intercepted over the public internet.
- Connecting with a site-to-site connection: traffic can be intercepted over the public internet.
- Connecting with a dedicated private connection: traffic cannot be intercepted over the public internet.
In scenario 1, the onus is on you to make sure your data is encrypted. In scenarios 2 and 3, your traffic is encrypted, but possibly crackable (however unlikely) by an outside party. In scenario 4, it's not even possible for an outside party to see the traffic. Just mentioning the fact that it is possible to intercept the traffic in scenarios 2 and 3 helps differentiate it from scenario 4.