i think that type of finger food eating sounds just great!
Smushing/mashing and sucking are brilliant ways for babies to get to know about finger foods. If he is putting things to his mouth then thats all you need for now! and swapping between finger foods and spoon feeding is fine too, let him hold something, while you spoon in the rest. Even help him try with a spoon (i recommend a plastic catchy bib for these times!)
My DS is 15 months now and finger food veggies still get chucked off the side of the highchair. It took him ages to get used to lumps, and still only eats dry lumpy things, soup with lumps for example is a no-go!! but he will eat fishfingers, potato, sweetcorn etc.
I think your DS is doing great, even without his corrected age taken into account. Just keep offereing finger foods as you are doing. And dont worry about nursery, he will do it all there even if he wont at home! they see all the other kids and want to join in!
Stay calm, and let the food fly!
Lili xx