[pavlov]

It’s probably organic. It often happens that the HN front page coalesces briefly on a theme. People see an article on a topic, research it a bit, and post what they find (or just repost something they remember from last week). And similarly it gets more upvotes on the “new” page because interest in the topic is active.

[Tangurena2]

This is called Baader-Meinhof Phenomenon [0][1]. Every time that you buy a new car, you see the same one everywhere you look: "hey! I just read one article about Tesla, here's 3 more!" when there is usually several articles each day about Tesla.

Notes:

0 - https://science.howstuffworks.com/life/inside-the-mind/human...

1 - https://en.wikipedia.org/wiki/Frequency_illusion