As a brief legal recap, in 1998 the DMCA added §512 [1] to US copyright law, which established a mechanism for shielding 'service providers' from liability for content posted by users (known as 'safe harbor'), but only as long as they follow formal procedures (known as 'DMCA takedown') to respond 'expeditiously' to remove content when they receive a notification claiming infringement, but also to restore access "not less than 10, nor more than 14, business days" after receiving a counter notification claiming the removal was a mistake.
In the post, GitHub implied they removed the youtube-dl repo after receiving the RIAA's formal takedown notice in order to 'comply with laws', and the law also required them to restore access after receiving the EFF's formal counter notice. However, the counter notice was sent yesterday and they restored access 1 day later, not waiting the legal minimum of 10 days. In restoring access so quickly GitHub isn't fully complying with §512, opening themselves up to liability if the RIAA decides to pursue legal action.
Perhaps a symbolic gesture to restore access a couple weeks before they would have been legally required to restore access anyway, but nonetheless interesting to see their willingness to set aside §512 safe harbor protections in the future if their reading of facts suggest a takedown claim doesn't have merit.