Sounds as though he may of did a partial acid start but the objective was the same to minimize the calcium dust. So it sounds as though it was successful.

An acid start is different than a standard chlorine start and bit more complicated. However, to do it properly, you should follow a set of steps which at the end includes raising the PH. So here is what I understand to be a proper acid start.

1) Add enough acid to drive total alkalinity down to 0. 8 Gallons sounds about right for 18,000 gallons but 4 was probably a bit less than needed. PH will drop considerably during this phase. This should be done within a 24 hour period if possible which is why a bunch of acid is added at once.
2) Most if not all of the calcium dust will dissolve during the next couple of days and the surface may soften a bit but should not dissolve so you want to avoid brushing at this step although at light brushing should be ok as well.
3) After 3-4 days, the PH should be up by now but if it isn't add enough borax to bring up to at least 6.8 and start the circulation pumps. Add chlorine as needed. Now you can start brushing.
4) After a week, maintain as normal. Some of the calcium may drop out of solution so you may need to backwash quite a bit over the next few weeks.

Acid starts are generally not a bad way to go but you need to make sure that the PH and alkalinity do not stay low for more than 5 days otherwise the surface may start to dissolve.