Not sure what’s going on but it isn’t right. The pattern is regular so I’d suggest it’s something with the structure not the paint. If it is fresh plaster then it may dry at different rates depending on what is behind it. Dot and dab would have cold bridges, drying slower which would match the pattern. Localised dampness in the plaster where it was colder and dried slower would affect the paint on top.
You’ve got a couple of options if you’ve paid already – see if the guy will come back to finish the job to a satisfactory standard. Do it yourself. I’d probably wait a few days to see what happens though – it might dry more uniform over a couple of weeks.
I would never specify the number of coats for a decorative interior finish. It doesn’t matter if it is 1,2,3 or more coats – what you specify is an acceptable aesthetic appearance and leave the painter to decide what that will entail and price/explain accordingly. Fresh plaster is different from recoating old paint and some colours have better hiding power than others.
Paint companies have got very good at formulating paints for different scenarios. I’d use a fresh plaster undercoat if one is available rather than a watered down mistcoat these days. I’d always say that you wait the recommended drying time between coats and follow the manufacturer instructions. As someone said above, it may be surface dry but not through dry. Putting another layer on top of paint that isn’t dry can lead to all sorts of problems as it does eventually dry. Thinks like cracking, crazing, wrinkling or just peeling off.
I’ve never seen the formulations for trade and domestic to compare. The idea is that the domestic stuff is easier to work with for someone who isn’t as skilled. It flows out better and is more tolerant to variation in application technique. I’ve also heard that the trade is made thicker as painters like to thin it back and they had problems with sagging.
All views/opinions my own and I should probably stop answering questions on her about paint for free!