In real life the "isst" would be slightly more pronounced because it's the action. He isn't sleeping, working or reading the paper etc., whereas "Sebastian ist am Tisch" would be relatively flat. It takes quite a bit of exposure to hear the difference though.....like with those nasty umlaut things!
I thought the sentence was "Sebastian isst ein Tisch" at first, and was very confused. :P
No, actually, "essen" (ich esse, du isst, er/sie/es isst, wir essen, ihr esst, sie/Sie essen) is very much human (neutral, actually, some German believe using a different word is specist); you're thinking about "fressen" (same conjugation) which could still be used about a human, but with offensive intent :)
I was thinking essen could be for eating like a human (passing food from hand to mouth, or using cutlery, etc) whereas fressen could be for eating food directly with your mouth. So it could be offensive, but could also be descriptive (for those juvenile or eager (trying not to be judgemental : -) people who like to dive in head-first). But I'm not a native German speaker. I was just trying to figure out the difference before I saw the "info" page about it. I may be wrong, but I like my definition : -)