In a networking discussion, L2 always means Layer 2. If the subject of caching came up the author would say "I'm talking about L2 cache here."

It's like TTL. It means one thing in a networking context but something totally different in a digital logic context.

But granted, somebody with no networking background wouldn't necessarily know that.

One can just add switch, router, network, etc to the query until it works. Supposedly they'll all work. Weak google fu means no info today, and if OP and the author are not the same person, then the latter may not even have a clue that it was posted on hn, where such high standards apply. If someone brought an electronics forum wiki post, should one expect every TLA¹ to be explained there too?

¹ Three Letter Acronym/Abbreviation