I don't know how it was done in Belgium, but I assume that they made their table beer the same way as was done for "small" or kid's beers throughout history, by fermenting the third runnings from a partigyle mash session.
This was big, iirc in medieval times up through colonial times, in places where the water was undrinkable, and the boiling, hopping and fermentation killed everything off (that's why we say no pathogens can grow in beer, btw) so the lowest ABV beers were reserved for the kids, and also as a common drink with meals and such.
They didn't sparge back then, just did three separate run offs of the wort from one mash tun.
It would be very difficult to do something like this with extract, I guess it could be done, but you'd be using very little....
You would best do it as an all grain...
Partigyle's are fun to do...Takes a little number crunching to figure...but you really don't have to..You could do a mid or low grav AG beer, and then run a second run through the tun to get your small beer.
Here's my thread on partyguiling which show how to "crunch the numbers" in figuring out a high grav and mid grav partigyle. I could have run a third "table beer" off of it as well.
This is a good thread, I think, because it show's how I went from not understanding the math of figuring it out, to finding getting it and calculating my recipe. Hope it helps.
https://www.homebrewtalk.com/f36/lets-partyyyy-gyle-pumpkin-porter-ale-one-mash-74927/