Are TB3 cables in any way different than USB-C cables? My company provided me a Lenovo USB-C dock when I received my Mac Book Pro 2017 model. That dock worked to a certain degree, but I happily replaced it with the Lenovo TB3 dock this week (which basically works much better, not having the quirks of the USB-C dock).

What caught my attention: the TB3 dock comes with a cable that has a "lightning" label (probably to indicate it can transmit power) and a "3" printed on it. 

Thing is: the USB-C cable is a bit longer (like 40 cm) whereas the TB3 cable is a bit shorter. So I tried connecting the dock using the longer cable ... and interestingly enough it worked, but one of my two monitors connected to the dock would stay dark. 

According to this here, USB-C cables should be "equivalent" (unless getting to long), but I just experienced something else.

Can anyone shed some light on this? Are there physical differences between these cables?
The "lightning" does not indicate that it can transmit power - it is actually the Thunderbolt logo indicating that it is a Thunderbolt cable.

All Thunderbolt 3 cables have USB-C connectors. Note that this is just the connector itself - it doesn't mean that the rest of the cable is the same.

Ordinary Thunderbolt 3 cables (i.e. cobber-based) also work as USB-C cables. In this manner they are compatible. You can buy optical Thunderbolt 3 cables (eg. if you want a 50 meter cable) - these are normally not usable as a USB-C cable.

On the other hand any USB-C cable is not Thunderbolt 3 compatible. It might be (as ordinary Thunderbolt 3 cables also work as USB-C cables). In general they are not.

The differences are mainly the design and quality of the cable, and to which standard they have been tested before leaving the factory. For example Thunderbolt 3-cables are generally specced to allow much higher amounts of power delivery than USB-C cables.