Sure you can argue the definition of alone but you’re splitting hairs. When people talk about being alone they’re referring to a lack of real-time interaction with other humans. Yes I rely on things built by other humans, that has nothing to do with being alone.
I quit my job last year and I’ve spent a lot of time alone since then. I don’t get lonely. I don’t crave human contact. I could easily thrive if I never interacted with another human ever again.
(Though someone inevitably suggested that there must have been some deep emotional trauma unconvinced women that made that man choose the wilderness.)
I think the drain from interacting with people for me largely comes from overthinking everything (and devoting a lot of mental energy to doing so in real time). But with replying to an online thread, I can take my time to make a reply I'm happy with, or flat out decided not to reply, which I do a lot (though I try not to if someone replied to me in a way which I could then reply to add to the conversation).
I also find the drain goes down as I build relationships and figure out the existing dynamics, and online forums give ample time for the latter to happen because I never feel compelled to get involved in the discussion before I'm ready.
Online discussions often also have the advantage of clearer feedback, though voting systems and blunt replies (where in person people tend to be less confrontational).