Yes it would be more akin to an internship rather than an apprenticeship. Also, contributing to open-source is not a learning experience like an apprenticeship can be. You cannot contribute to FOSS without a minimal skill level. Whereas, you can enter an apprenticeship from scratch.

Whether or not you agree with apprenticeship systems being good or bad, it is clear that the GP comment on FOSS being a replacement for an apprenticeship system is wrong.