I guess he either boasting it or making up the number then ( ..or could be he forgot the actual number since it's been a while )
He did confirmed that he is using eAthena, and his server is Malaysian-based. The server name is DemonicRoseRO which sometimes referred to as Melaka RO or IceAge RO.
It's very interesting to know that 30k concurrent connections are possible for non-commercial server, because this is the main 'bullet' for me to shoot his claim down
Though...in light of what you guys have highlighted plus the extra handicaps he gave to himself ( It's in 2005, server is a single Pentium 4 PC, hosted from his home using consumer level broadband which that time is ~1Mbps top ( plus it's ADSL, the upload is way less than that ), all players in one area, it's during WoE, and so on ) I guess it's just not plausible.
Thank you for all your input guys, really appreciate it ~~~