So the facts we know are that 1) Samsung market share rising from 23% to 31% and 2) they recently released new foldable phones. But do we know that's the actual primary reason for the increase? I couldn't tell that from the article. The article mentions engagement of specific social media posts, but that's as much as it, without any sales number/estimates from anyone.
Just anecdotally I spent some time with older members of my family a couple months back in a hospice situation, and folding phones were very popular with everyone at the facility. If your vision isn't the best and maybe your hands aren't so steady, having double the real estate makes a big difference.
Funny I saw someone who's phone was so zoomed in the letters were massive in the messaging app, I thought they mistakenly did that but it was on purpose.