My understanding is that the treading means that you can upload multiple files at the same time to improve efficiency if the source system is capable of running in that manner.
For CloudWatch there would will only be entries if you have enable CloudTrail to log to CloudWatch. This would monitor management and data level actions and wouldn't matter if multi-tread or multi-part from what i've seen.
I work with PHP more than Python but AWS provide very useful SDKs for the majority of their services: https://aws.amazon.com/developer/language/python/
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