Most network software for DOS was LAN-oriented, like Novell or NetBIOS. Just drive mapping and printer redirection. I'm not aware of a TCP/IP connectivity suite being available for DOS in that era, and I'm not sure how it would have worked given that DOS provided no networking libraries to hook into.

Oh I wasn't trying to reverse-engineer his network from that comment, just saying that this was a thing that was possible and that people did at the time.

I agree it's highly unlikely that the AT was running slirp. Wikipedia says an AT was a 286, so it wouldn't have been linux. Not even sure what the options would have been. Minix? Xenix?

QModem ran on DOS, so the AT wasn't running UNIX. It's almost certainly being used as a terminal.

I can confirm that they did run Minix OK, although I remember the network support was iffy at best. We never got it to work at any rate. XENIX would have been hard to get your hands on. I think QNX would run on an AT as well, although my memory might be playing tricks on me there.

Xenix definitely ran on a 286. I can't say re: Minix-- I never have used it (though I probably should just to have the experience). I believe there was a Crynwr SLIP packet driver.