Recently I've found out that copyright owners are claiming profits of YouTube videos where allegedly their content is used. Specifically, this video was claimed to be a copyright infringement.
I'm aware of other questions related to copyright and YouTube policies, however my question is very specific. In the claimed video YouTuber plays on acoustic guitar for 25 seconds without even singing what for me looks like a quotation.
Is there anything in US copyright law regulating how long and in which exact form (exact record or performance etc.) a musical quote can be, if such concept is a thing at all? While this video is on a commercial channel it's quite evident that guy did it for educational purposes.