MacBook – charge a power bank through charging MacBook

No. The Thunderbolt port does not supply power to the laptop. The only way to provide power is through the MagSafe connector.

As with any computer, using a higher-wattage power adapter is fine, but using a lower-wattage one might not let it run at full efficiency and may be unhealthy for the battery in the long term. (And of course it won't charge as fast.)

There are a number of answers to this same question, but for MagSafe chargers, here. Kuba Ober's answer goes into quite a bit of detail about it, though I can't personally vouch for its accuracy.